[Pukowski] Ecological Investigation of Necrophorus F., 1933

8/7/2019 [Pukowski] Ecological Investigation of Necrophorus F., 1933

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FOREWORD

"I thank Dr. Derek Sikes for his help in obtaining this translation of Pukowski's

classic 1933 paper on Nicrophorus.

The text is thorough and very detailed and a link to a succinct summary

is to be found in the Table of Contents labelled 'SUMMARY'."

A Dale,

http://www.bugsandweeds.co.uk

ENGLISH TRANSLATION OF PUKOWSKI'S 1933 NICROPHORUS PAPER

The following was translated from the German by Janet Christie and originally posted

by Derek Sikes. Refer to the original document for literature cited, tables and figures,

which are not included here. This reproduction is not to be used for any purpose other

than private study, scholarship, or research.


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Ecological Investigation of Necrophorus F.

-

by

Erna Pukowski

Zeitschrift fur Morphologie und Oekologie

der Tiere 27(3): 518-586. 1933.


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TABLE OF CONTENTS

INTRODUCTION

RESULTS

A. General Life of the Adult

1. Occurrence -- frequency

2. Environment

3. Temporal occurence

4. Nutrition

B. Reproductive Biology

1. Relationship of beetles to one another

a. Attraction of females

b. The isolation of pairs from a large number of

individuals end the resulting conclusion

c. Ecology of the fight

d. Fight with strange species or races of

gravedigger

e. Course of the fight

f. Relations between partners of the pairs

2. Relations of the beetles to their offspring

a. Brood care

b. Burying of a body

c. Rounding of the body and completion of the

crypt

d. Egglaying

e. Moisture and digestion of the body

f. Male participation in brood care

g. The brood at the time of larval development

h. Feeding of the larvae

i. Ecology of feeding

j. Defense of the larvae and their food

k. Maintenance of the cryptl. Defense of males at the nursing

m. Development of full-grown larvae to young beetles

SUMMARY


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INTRODUCTION

The striking instinct of gravediggers (Necrophorus fabricuis) to bury small animals was first

reported by Gleditsch (1752) with the help of experiments, in which development of beetles

with different species of small animal corpses at their disposal was observed. Gleditsch

succeeded in putting the burywork of the gravediggers in relation to their reproduction. On

the suggestion of these chemists Melim from Bremer (1755) who independent of the

mentioned report, followed the burial of a mole by the gravedigger and recognized in them

the remarkable broodcare, which also occupied A. I. Rosel von Rosenhof (1761) with the

remarkable life of the gravedigger. We find his result put down in the celebrated "In

sektenbelustigung" equipped with coloured pictures of adults, larvae and pupae.

From the statement of Gleditsch (1752) that a gravedigger had brought a stick to undermining

to collapse was fed on the body of a toad, Lacordaire concluded about the intelligence of this

beetle. First the French researcher J. H. Fabre destroyed the fable of the intelligence of the

gravedigger while he showed with the help of numerous carefully carried-out experiments

that the actions of this animal are fixed within the setting of instinct, but not as was first

interpreted a reasoned thought.

If the experiments of Fabre lead to greater clarity so too a new problem escaped his

observations that researchers had perceived as such, but not been able to solve. This new

problem lies in the fact that on the buried carrion there always remains a single pair of

gravediggers, highly suitably, even if more beetles worked at it. The question of how this

appearance is to be explained was discussed recently in terms of animal psychology and

sociology (Renter 1913, Schroder 1929) however until now no satisfactory solution was

found. On the suggestion of my highly revered lecturer, Herr Geheimen Regierungsratses

(private administrator adviser) Prof. Dr. zur Strarsen, I put the solution of named problem to

the test.

Fulfillment of the task required most precise knowledge of the whole digging event withinwhich the isolation of pairs from a larger number of individuals must take place; this could

only be achieved through extensive experiments preferably under natural conditions. For this

reason I have investigated in depth the general ecology of the genus Necrophorus.

The experiments were carried out on the following species: Necrophorus germanicus L.,

humator B1., vesplllo L., vespilloides Herbst, investigator Zett, fossor Er. (interruptus Steph.)

The species germanicus, was sent to me mostly from Danzig; I baited the other animals

around Frankfurt a.M.

RESULTS

A. General Life of the Adult

1. Occurrence - frequency.

Although around Frankfurt not all species of the genus Necrophorus occur, humator, vespillo,

vespilloides, fossor and investigator still occur with certainty. The first three species are found

in large quantity, and investigator and fossor in smaller quantity. N. germanicus is scarce and

N. vestigator even more so.

In order to catch the gravediggers, I arranged measures of bait in the following state: a pail,

whose base was perforated for the draining of rainwater filled to 10-15 cm with earth. Inside a

slightly decaying large piece of meat was laid and the entire pail was put so that it is not

exposed to direct sunbeams, yet still breezy enough for the smell of the carrion to flow about

unhindered. Beetles flying by are easily able to attain the body; but there they are caught for


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the narrow limit of space left them is too little for flying away and they are not able to

clamber up the smooth and steep walls of the pail. Besides few make attempts to fly for there

they find rich booty and the soil layer offers them the possibility of shelter. Every 10-14 days

the traps were baited with inew meat, and were able to be used continuously in this way.

In order to give a rough impression of the frequency of the gravediggers, I have included 3

tables which give again the total yields of the baits. The catch was made after the meat had

layed out for 3-4 days in warm weather. On baits M.S., M.E. and M.W. named beetle species

in the following numbers were found. From this set up it is obvious that the gravediggers are

by no means as rare as one accepted from chance finding.

2. Environment

The searching of numerous baits gave me the opportunity to study the occurrence of frequent

species (humator, vespillo, vespilloides) around Frankfurt a.M. with regard to their

environment and to confirm the winning conception with a systematically employed series of

experiments. The traps were put out in different areas of the nearer and farther surroundings

of Frankfurt, and the caught animals registered with time, numbers and species. Data in Table1 are from a large series of arbitrary catches. The baits are labelled with the numbers I-VI. All

catches given here were made at the same time of year, namely mid Mav 1931. M (bait) I and

M II were in Tannus near Eppstein. Distant mixed woodland (Pinus and Fagus) is the near

and far environment. M III and M IV were in meadows at Ginnheim and Rodelheim in

Niddatal which stretches to the foot of Tannus. M V stood in the middle of a large, very dry

confer wood area in Frankfurter Stadtwald. M VI lay in mixed woodland (Pinus, Picea,

Fagus) in Walldorf and close to the woodedge not far from extensive meadowland. So M VI

joined the environmental conditions of previously chosen places.

From Table I in mixed woodland from Eppstein at M I and II altogether 41 individuals of

humator and 36 of vespilloides were found, but not a single example of vespillo. Forty-four

examples of N. vespillo were found from meadows at Ginnheim and Rodelheim in M III andM IV. However M III and M IV show uniform vespillo- material. The yield in pine stock

brings a new species picture. Here in M V the domination of N. vespilloides really comes to

light. Only at M VI are the three N. species commonly found.

This proves that the findings of the single catching points at the same time of year concerning

the species distribution are by no means all equal to each other. Rather it looks as though

clearly there is a factor governing the occurrence in appearance: The habitat of N. vespillo is

meadowland, while humator and vespilloides are indigenous to woodland. M VI supports as

its surroundings are mixed woodland as well as meadow, the importance of control

experiments. Correspondingly examples are found of humator and vespilloides which come

from the adjoining meadow. Those in the mid-part of the table containing beetle numbers

perhaps appear scarce. But the unquoted records of the same year (1931) as well as therecords for 1929, 1930, and 1932, extend the total to 2357 examples, and corroborate the

reported results, eliminating the probability that these patterns are due to chance alone.

Naturally, the membership of a species to a clearly defined environment from the records

must be all the clearer, all any time a habitat and untroubled from strange intruders opposed to

them. For the species vespillo it was possible to employ a trial experiment in a handy absolute

territory. It was carried out in Freistaat Danzig at a place where there is no woodland for

many kilometres in circumference. The experiment caught 64 examples of N. vespillo and

one of N. vestigator. Trapping in Freistaat Danzig, on different ground confirmed the

Frankfurt results. It was possible in Frankfurt in spite of little expansion of affiliated areas, to

construct a correlation of species and environment showing a considerable environmental

loyalty of the species. This applies particularly to N. humator and N. vespilloides, which in


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general were found not more than about 100 m distance from woodedge; while vespillo

advanced a kilometer into the woods.

The results from M V in Table I indicate that N. vespilloides is found predominantly in stands

of confer wood. Hence its occurrence in mixed wood was due to the presence of scattered

pine stands while N. humator occurred particularly in deciduous woods. Although this

hypothesis is supported by numerous results, isolated results still occur which directly

contradict this. A moment on the ecology of Nicrophorus however helps to eliminate the

apparent contradiction. Because the gravedigger buries small carrion as food for the

descendants, they are dependent upon the condition of the ground which offers unequal

resistance depending upon the material covering the ground. The conifer woods, which appear

as pine woods in a large part of the Frankfurt area, stand here on predominantly very dry,

sandy ground. The ground is almost free from rooted plants, covered with an even rough

humus layer of needle litter which is interrupted here and there by small moss lawns

(Hypnum, Polystichum species). Elsewhere the ground is damp,deciduous leaf woods, which

in west Germany is mostly dark brown to black crumbling humus with a far higher moisture

content than the sandy ground of pinewoods. Its covering with leaf-litter and loosely twisted

roots of ground plants, is about average in resistance to mechanical destruction fallingbetween the loose leaf litter of pinewood and the dense layer of roots of meadows. The

ground of valley meadows (and only these are common here) is heavy and moist to wet. It

bears an extremely dense root layer of its predominantly Gramineae covering.

The described soils differ so strongly from one another in their condition that it was

understandable, when every N. species preferred for digging capability and behavior an

adequate environment. There is also clay-sandy deciduous wood soil and moist to marshy

pine wood soil. At such;places. the picture appears reversed exceptionally. In wet pinewood

N.humator rules but in dry deciduous wood N. vespilloldes does thus accounting for the

above contradiction. The exception offers the best proof that the ground is the primary habitat

characteristic for the-gravedigger.

Extreme differences from the rules are rare in the Frankfurt area. More frequently one finds

that the relative population between N.vespilloides and N.humator in mixed woodland shifts

in favor of one or other sides only somewhat. according to whether the experiment was put in

a dry, sandy or a more damp, humus mixed wood. For example the yield from M I and M II in

mixed woodland of the Tannus in Table I shows the proportion 41:36 where N. humator

forms the larger quantity. In mixed wood of sandy urban woods likewise both species are

found, but in totally changed proportion (Results M.S. S.520), 7 N. humator and 69 N.

vespilloides. The sample numbers of N. vespillo from adjacent meadowland were approached

in the woods.

3. Temporal occurrence

The baits were visited during the warmer times of the year for Necrophorus species. The more

or less early time appearance of beetles in the spring as with their disappearance in autumn is

naturally dependent on favorable or unfavorable weather. In 1930, the spring was warm, and

on 4 April the first gravedigger, N. humator, although the bait was on the edge of a small,

damp deciduous wood in the middle of a further stretch of meadow equally favorable to N.

vespillo. N. vespillo appeared for the first time that year 16 days later. Due to cold springs in

1931 and 1932 I cannot say what the average date of appearance is. In both cases the animals

did not appear until May and they were caught at the same time. While N. humator, N.

vespillo and N. vespilloides appear at approximately the same time and also disappear to

hibernate at the same time. N. investigator and N. fossor (interruptus) make a striking

exception. These species were not found until the end of June or beginning of July during all

three summers of the study (1930, 1931, 1932). The late appearance of these species is

connected with their individual cycles which are delayed for months in relation to the 3 other


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species, N. humator, N. vespillo, N. vespilloides. On particularly warm November days one

finds here and there flying Necrophorus but as a rule, all species begin their hibernation

around the beginning to middle of Octoher.

Although gravediggers were recorded as common animals, one rarely finds them without the

aid of bait. This is based on their nocturnal life style. The gravedigger comes out of the

ground in which he has been secreted for the day, around sunset. If one observes this

happening, one sees as with a small shake of the ground two appearing antennae. Apparently

the beetle examines the environment through his smelling organs. After that the animal leaves

the sheltered province and climbs any blade of grass. In spite of his size and weight he brings

this about with dexterity. If the grass bends to the ground under his weight, another blade is

climbed. Apparently, the beetle operates by instinct, to raise himself somewhat above ground

level. In this way he manages to contact initially the light scents from possible food and

secondly he can lighten himself for take-off. There he remains sitting preening himself with

antennae moving, ready to begin his flight in search of food.

The gravediggers are pronounced dusk and night animals when living in a well maintained

terrarium of 50-60 beetles and only rarely does one appear in the daytime. If theenvironmental conditions are unfavorable for the beetles, e.g. strong sunlight, high

temperature, extreme drought, narrowness of cage and lack of food, they are driven to the

surface during the daytime. They then undertake rapid running around and continual attempts

to escape in which they fly round wildly. These are however clear reactions to abnormal

conditions.

In certain cases the Necrophorus can indeed be found also during the day in natural

conditions. Every animal which has found carrion at night stays there during the day. There

they hide on the underside or slide inside in some which contain cavities within, where they

are able to devote themselves to undisturbed feeding. Often on windy but sunny spring or late

autumn days, thus shortly before or after the winter hibernation of the animals, one sees flying

Necrophorus. Probably they are driven to it by the hunger, and that at all times of the night itis too cold to search for food.

Their life in the dark of night or the soil makes the gravedigger correspondingly sensitive to

bright light, yet the degree of sensitivity varies with the individual. Most times they retire into

the soil with sudden lighting with white light individual answers to a strong light attraction

done with Thanabos. Others again are not disturbed in their occupation. In strongly softened

light one can observe almost all individuals undisturbed. For this reason this sort of

illumination was employed chiefly for observation.

4. Nutrition

In quick flights, thereby frequent and uninterrupted in varying direction, the gravediggerswander through woods and meadow till the wind carries to them the scent of carrion. At once

the flight stops, flying round the source of the smell in narrow circles and finally land on it or

in their near surroundings. In the last case one sees the beetle hurrying to his find with

swinging antennae.

Although the Necrophorus lets himself be enticed to the scent of carrion, they are not

exclusively carrion eaters, but predominantly predators. Already more than lOO years ago an

English researcher, Bell, observed how gravediggers seized and consumed the fly larvae from

a carcass. The description of this event, which was first published in 1873, has remained

unnoticed and still long afterwards Necrophorus is reported as a typical carrion eater. Later

Ch. U. Clark (1895) and W. T. Davis 1915 often have called attention to the predatory life

style. Most recently F. Steele (1927) showed this in a perfect series of experiments on the

North American gravediggers describing the facts of eating charmingly and vividly.


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My experiments showing the preference for diptera larvae by European species is of value. It

was especially pointed out that also N. vespilloides is no exception to the pattern of nutritional

habits. The fact that this species was sometimes found in rotten woodland fungi, gave

occasion to the statement (Chenu and Desmarest 1851), that N. vespilloides did not feed from

carrion but only from fungi. But that is not true. Although these gravediggers were enticed

through the smell to decomposing fungi, they were still only hunting for the living diptera

larvae in the fungus. I saw a hungry male of this species consume 17 maggots in 35 minutes

after which the meal was interrupted.

The predatory nature of the genus Necrophorus is clearest expressed in the species N.

germanicus. In the night, this large, extremely agile animal hunts for Geotrupes unless fly

maggots are within reach. Klungelhoffer (1843) and Schmidt (1883) always observed a fierce

struggle between N. germanicus and Geotrupes (mutator) stercorarius and both concluded

from that the predatory life style of N. germanicus. This conjecture I was able to confirm. I

went along the following train of thought: If those observed cases from the above metioned

authors are not chance records, particulary N. germanicus, rather instinctive hunting for

Geotrupes it must be expected that it reacts to the smell of horse dung the typical habitat oftheir prey--as N. vespilloides reacts to the smell of fung. In order to prove this, the following

experiment was set up.: In a round terrarium (lOOx94x58 cm) in which several N. germanicus

were held, I brought some horse dung. The Necrophorus, which until this moment were

wandering round apparently aimlessly in the cage, stopped with antennae beating keenly or

others immediately began their direction of marching and hurried to the dung heap. This is

possibly explained by the water or bacterial content in the fresh dung attracting the

Necrophorus to approach. That however contradicts the behavior of the beetle when they have

approached the source of the smell. None of them bite into the heap with their mandibles,

rather all run as if searching it over and turn around now and again a large piece of dung with

head and thorax. One cannot keep the false impression as these animals search the dung for its

occupants. Single individuals withdraw, the majority however remain at the site and bury

themselves superficially in the dung. One particularly lively female hid for example under alump of dung. Only the head with perceiving antennae, was still to be seen. At this point I

would like to take the opportunity to mention an observation of V. Lengearcken, who found a

N. germanicus under a ball of horse dung lying in the wild. Animal and dung ball were

already sunk somewhat into the ground. Undoubtedly it had to do with the same event which I

was able to observe in the terrarium. There also I saw here and there how the dung was sunk

somewhat into the earth through the agitation beneath the beetle.

So the beetles remain to a certain extent in ambush, only alternating now and then hastily

leaving his place. This behaviour of the beetle then follows without there being any Geotrupes

in the cage or in the vicinity! After a fresh dung pat is searched through for the Geotrupes by

N. germanicus, they wait for the moment which enticed hy the smell of dung, happens with

all probablity in a short time.

Now I placed about 60 Geotrupes into the terrarium. All belonged to the species G. sylvaticus,

which I was able to collect most easily in the surroundings of Frankfurt. Nearly all the dung

beetles groped about for a long time at the nearest way of the dung heap. Scarcely had the

first reached their goal when those still inanimate predators became lively, appearing in

masses. Everywhere the large predatory gravediggers claimed their prey which to begin with

chirped loudly, but desperately, to defend themselves. Also the previously mentioned female

left its place under the dungball and hurried smartly towards the near prey by the shortest

route. N. germanicus attacked its prey not from ambush as one would presume from its initial

behavior but hurried openly to his prey and seized it with legs and mandibles. Every caution

appeared totally useless as the observer did not receive the impression that Geotrupes

sylvaticus was able to recognize his enemy as such. One sees on the contrary the dung beetles

marching on the Necrophorus and even in direct proximity no impression was noticeable.


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That what took place now between the attacker and his prey can by no means be described as

a struggle. For both animals are too unequal in strength and quickness. N. germanicus seized

the weaker, G. sylvaticus with both legs and thereby threw itself on the back or the side. This

pose was taken willingly as the eating of large fly maggots, so that more than half of the

gravediggers can be found after a feed with these larvae, the prey held in front of them

between first and second pairs of legs. Small fly larvae are nevertheless held free in the

mandibles.

Through the extremely tight hold of predators, Geotrupes sylvaticus becomes pressed against

the ventral side of its opponent and can be eaten conveniently. One hears loudly between the

weakening chirping of the dung beetles cracking of the chitin armor under the strong

mandibles of the gravediggers. At some point the outer skeleton becomes broken. In the

majority of observed cases the prey was slit open on the ventral side of the area between pro-

and meso-thorax. In other cases the predator succeeded in destroying the strongly chitinized

(thorax) neck plate. Once the body is open, the organs are pulled out and eaten. In the course

of half an hour I saw one N. germanicus male seize and consume five Geotrupes in the

described way. The others who were no less lucky in their hunting so that the remainder of theGeotrupes lay around everywhere in the terrarium. The N. germanicus seizes the dung beetles

so quickly when hungry, but they are indifferent to them in the satiated state, hurrying by

without any attempted attacks on the Geotrupes.

The experiment was performed several times with the same results: N. germanicus habitually

hunts for Geotrupes! To be sure, fly maggots and Geotrupes were offered to them at the same

time and as a rule the fly maggots were preferred.

In spite of their preference for living prey Necrophorus show only a slight inclination for

cannabalism. Healthy individuals did not cannabalize others when very hungry and under

confined living conditions. An exception to this may arise in fresh, recently colored young

beetles which at times consume uncolored individuals--usually brothers and sisters. This isseen only in rearing under artificial conditions,indicating environmental conditions as

causative factors. While in nature the beetle immediately goes out in search of food after

leaving the pupal stage, in the terrarium he is held back by enormously limited room. From

deficiency in other food the animal seizes conspecifics which are convenient prey for him.

This was easy to prevent; shortly before the hatching of the beetles some meat was put in the

cage. Still in nature, cannabalism can occasionally be observed, when sick or hadly injured

individuals are attacked and consumed.

Besides the predatory nutritional ways all here-mentioned, Necrophorus species are also

carrion eaters. As Steele (1927) already mentioned for the North American species, he

showed the little decayed food of the strongly decomposed. Largely independent of the type

of meat, the Necrophorus accept every kind of carrion that is offered to them. Meat or internalorgans of vertebrates such as sheep, pigs, beef, horse or even tiger and turtle soup whose

bodies were placed at my disposal by chance served the gravediggers for food just as the

bodies of small vertebrates or even many invertebrates like earthworms, slugs, and larger

insects. When one puts a hungry animal on a piece of meat, it tests the food here and there

with antennae and mouth appendages. In a somewhat damp and soaking place one sees it stick

to and drive in its mandibles. The choice of place to eat corresponds to completely the

preference of the gravedigger, on small vertebrate bodies firstly the body opening, eyes or

possibly wounds as this also Steele (1927) was able to establish for those species which he

had examined. Yet without having a visible ingredient cut off, the jaw becomes open again, in

order to immediately grip to new dense area behind the place again, a match that is repeated

so long with between the mandibles rises a weak border of ordered meat. One sees the mouth

appendages working this border again and again. After a long time, often after an hour, the

beetle turns to another place, without that, that border would have completely disappeared.


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If one now disturbs the animal in some way, it vomits immediately a part of the food taken

up, in which from microscopic examination are traced no formed ingredients. Therefore the

meat is not devoured in small pieces, particularly rather milled through and pressed out by

continual work of the mouth appendages to then take up the food in liquid form. The tough

and hard tissue stays behind, as it also happens in the-consumption of a diptera larva whose

cuticle stays behind--when also in young larvae till crushed to an unrecognisable state.

Besides the mechanical work to gain liquid food, it would be possible that the material

becomes liquified through the effect of a deposited extraintestinal gut secretions. Although

the vomiting of a digestive secretion was not able to be explained up till now, certain

observations and considerations make the surmised events probable: A fresh piece of insect

from which a Necrophorus had eaten showed for a long time at the eating place distinct

alteration. Brown color and jelly-like blurred contrasted the place clearly with almost

unaltered surroundings. Further speaks the admitted factor, that disturbed gravediggers vomit

intestine contents, respectively intestinal secretions for the operation of a preoral digestion

during meals; to us this appearance is faced only in beetles with extraintestinal digestion.

Further evidence for this species the food in-take by the nearest relations of the gravediggers,

the Silphinae, is wide, as Heymons and V. Lengercken pointed out (1926-1932).

B. Reproductive Biology

1. Relationship of beetles to one another.

a) Attraction of females

In May the species N. vespillo, N. vespilloides, N. humator, and N. germanicus, in August the

species N. investigator, N. fossor are already in reproduction. At this time the beetles begin

with that activity to which their name gravedigger points: they bury small carrion in the soil in

order to receive it as food for their descendants. Their gonads have developed immensely to a

mature state, and both sexes happen now on the search for carrion that corresponds to thedemand of their broodcare instincts, and describes at the same time the meeting-place for

males and females. When a body is found and a pair are together then the preconditions for

reproduction are fulfilled.

If only a male arrives at the carrion, one can make the following highly remarkable

observation: the males which initially set about the digging work, break it off after a short

time in an effort to reach a high point in the immediate vicinity of digging. The male climbs,a

blade of grass, a stone or even a small heap of soil, for want of a high lying point. In all

observed cases this is commonly a very surprising pose which

the male assumes. The animal orients itself so that the head is as low as possible but the

abdomen stands as high as possible in space. The head is thereby bowed so low that themandibles often rest on base, grass stalk, stone or soil. The whole body, which normally

shows in every Necrophorus in front of as well as behind a distinct slope from the ventral

aspect, becomes extended in a slope from behind causing a steep angle. The body weight

thereby rests on fore and middle tarsi, while the hindlegs are only lightly placed or even held

freely suspended. The hind end of the body is so strongly extended that the abdomen appears

longer and more slender and the last segment which normally lies hidden in the body appears.

In this position the male persists, refraining from short breaks without clearly visible

alteration for more than an hour. Only the tip of the abdomen betrays slight swinging or

rotating movement; the last segment stretches away from the others occasionally revealing the

intersegmental membrane. I would like to describe this strange operation as the "Ventilation"

of gravediggers.


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What ecological meaning comes from the "ventilation" of male gravediggers? I was able to

observe it 13 times, the results of which are summarized below.

1) The "ventilation" was regularly performed in the immediate vicinity of a carcass.

2) Ventilating animals were without exception males with ripe, plump full testes.

3) Never was a female observed in the vicinity.

4) Only on warm summer evenings (June, July, August) after sunset was ventilation able to be

observed.

These facts suggest "ventilation" of male gravediggers involves the females. Presumably

flowing from either the tip of the abdomen or the intersegmental membranes are sex or

species specific scent to signal passing females and to guide their approach. This assumption

is supported in that at times one sees both sexes coming to the carrion's scent. When the

carrion is buried superficially by the male, thereby checking the enticing smells, the sex scent

of the males was able to lure a female; a peculiar profit results for the prey is protected fromany other carrion eaters, and remains reserved in all probability for the species.

The declared explanation also found experimental confirmation in degrees: after a series of

failed experiments I succeeded finally in two cases in bringing to puberty males isolated on a

carcass to "ventilate." That this experiment frequently failed, I believe goes back to the

artificial environmental conditions. Out of the obvious assumption that the above mentioned

points 1-4 are taken from, the size of the cage (my successful exp. were carried out in a cage

of the dimensions of lOOx94x58 cm) and above all good ventilation are important in success.

So the term "ventilation" in the gravedigger ought to be authorized. Still it ought to be pointed

out that a Necrophorus is not designed for a such extreme placement of the abdomen in

ventilation. Although the movement of the hind body is not equal to that of Hymenoptera--astill striking apparent convergence finds the ventilation of gravediggers remaining like the

termites. From Tollin (1862) a male termite that has found no partner through swarming who

scarcely had begun digging work, stretched the abdomen in the air and stuck to it for many

hours each day.

b. The isolation of pairs from a large number of individuals and the resulting conclusion.

When a male and female of the same species meet on a suitable body for broodcare (or the

body has been found by an already paired female (vgl. S 539) the carrion is buried and serves

the larvae as food, till they are full grown and move further into the soil for the pupation. At

this time the store is consumed until from insignificant amount remaining, has sufficed even

for the brood's parents. But what happens if the same quantity of food has to suffice for thebrood of several females? Without doubt the development of all larvae would be greatly

endangered through shortage of food. This danger is likely -for it happens often enough, that

through the smell of the carrion several females are attracted with mature~ ovaries. How is

the threatened danger averted?

J. H. Fabre (1899), as I have already mentioned in the introduction, made the striking

statement that he never found several females on buried carcasses. Always he mentions only

one pair there, even if beforehand more than two individuals had been working at the digging

at the same time. My first task was to examine this declaration of Fabre for its accuracy.

Fabre, known as a sophisticated observer, remains to be considered for this observational

experiment on Necrophorus which was carried out in an aviary, therefore under artificial

conditions, with only a limited number of beetles, namely 14 individuals. The question which


12/37

I had to answer ran accordingly: is only one single pair really found on buried carrion in all

cases, including under natural conditions?

All my experiments were made correspondingly in natural conditions--thus they were not

successful. Through laying out suitable pieces of meat to attract the grave diggers, they were

allowed to bury the prey undisturbed and after a known time the number of beetles remaining

on the carrion was checked by digging it up. Digging up is too crude a method. Through the

warning of shaking the ground, many beetles hide further into the soil and cannot be found

and cautious digging is very time- consuming.

In order to avoid this disadvantage, 200 flower-pots (12 cm high, 14 cm diem. at top) were

distributed in woods and meadows in the surroundings of Frankfurt. They were sunk in the

soil to the upper edge and filled with dug material till full, after the base of the vessel was

covered with a fine mesh wire net, to prevent the escape of beetles from beneath (Abb. 3). A

small piece of meat about the size of a mouse was laid on the soil in the flower pot. On a

small adjacent piece of wood a number was marked under which the results were entered in

the records. The experimental site was visited several days in succession and observations

made on them continuously registered. After the meat was sunk into the ground, through thework of grave diggers. I waited 2-3 days, then dug the flower pots from the ground and over

turned them on a firm base. Its contents lay exposed in this experimental procedure and could

be searched through without trouble, which is also of importance for later mentioned

observations. Escape of beetles was excluded through this arrangement.

Although not all 200 experimental sites were in operation simultaneously (for the meat was

eaten frequently by other animals or carried off by the gravediggers), I was still able to

examine in the course of Summer 1930, 254 cases in the described way. An experiment was

only counted then, when the carrion was found already in a subterranean hole, which Fabre

called the crypt, there in the presence of this crypt for sole proof for the termination of

digging work is recognized. The examination gave the following results.

In 197 of the mentioned cases a pair was found on the carrion or in the near vicinity within

the flower-pot; in 53 cases, I was able only to find a female. In 4 cases I found in the near

vicinity of the crypt 2 females (which by further investigation proved to be sexually mature).

My experiment then proved perfectly that really only 1 female remains behind on the buried

carrion and it has in the great majority of cases the male with it. The number of exceptions is

so small that they may be neglected. Also it ought to be emphasized that the results were not

being influenced substantially perhaps by the lack of competitors: in most cases more distant

individuals were found in a small distance outside the flower pot in the soil.

If the initially asked question is answered in the affirmative, we are faced secondly with the

problem of how the separation of a single pair is brought about from a large number of

available candidates. This looks as if it involves animal psychology. But the apparentlypuzzling occurrence is clarified through broader consideration. The grave diggers dispute

their right to possession of the carrion by fighting one another, and it is predominantly

individuals of the same sex which fight.

The description of a typical start to an experiment comments on the cause of events in detail.

In a spacious terrarium, 4 pairs of the species N. vespillo were introduced. Every female was

marked with a color mark on the pronotum. All males received at the same time in the same

color (white, light blue, light green and yellow) a mark on the elytra so one was able to

recognize again at a glance the sex of the animal and at the same time the individual. The

pairs were first confined to this experiment after they, separated from the others, had proved

their sexual maturity through desire to dig.


13/37

On the day when the animals were committed resting onto the soil, I layed a dead mole on the

soil surface in the middle of the cage. At sunset the first female (bright blue) appeared and

hurried to the mole, climbed and clambered around on it, in order to disappear. Here & there

the shaking of the dead body showed that the female was digging. Meanwhile the light green

and yellow females also turned up. While the first ran here and there the corner of the cage,

the yellow male marched smelling to the carrion. Arriving there it soon slipped under the

body. While for several minutes nothing happened, till both animals, the bright blue female

and the yellow male by chance at the same time came forth from under the mole, each at a

different place. Now the female scent appears to come from the new comer (male). The

female pauses visibly and runs directly to the male with quick steps, hesitates, reaches with

the antennae the abdominal tip, that aggravates him, as the male has quickly hurried over by

the approach of the female. Scarcely has the female succeeded in testing the hind end of male

with tasting tips of the antennae, than it turns away. Then the male begins to follow the

female. With a few, hasty skips it stops, a little shake with the antenna and with the loud

chirping of both animals, mating takes place. After that the pair turn toward their work again.

In the corner of the terrarium, the second female appears level with the soil. It bears a white

color on the neck plate and is already well known to me because of its strength andsavageness. This beetle also goes to the carrion immediately and meets there with the female.

Both go immediately one after another and both appear to recognize the smell of the hind end

of the body of the sex of opponents. The movement of the grave digger at their work

particularly on warm summer evenings was described already, and quickly mentioned, yet the

aggressive savageness surprises so, with those in the situation the two females rushed at one

another. The fight begins.

But, scarcely begun, it is already finished. The bright blue female, which at first had taken

possession of the mole, left the place of the fight in a rush to escape. It searched the walls of

cage and clambered at them, and as this did not succeed, it buried itself in the furthest corner.

It was to be seen no more for the rest of the evening. The strong female with the white mark

now crept under the mole where meanwhile the male was pursuing his work. The victoriousfemale thus thrust aside the loser, and took possession of the prey itself. Soon it emerged

again a few cm distance from the body. Close examination showed that it had created a

passage, which began under the mole and ran to the surface here. One is reminded of passages

which lead from the inside of old fortresses to freedom. In this security the female remains

sitting till hidden to head and forelegs in the soil, and throws itself from here out onto every

grave digger which wants to approach the carrion. First it is the light blue female that comes

that way. Although after itself, the female has information about the sex of the approaching

animal, it creeps under the carrion, and turns up there shortly again in the mouth of its

subterranean passage. The newly arrived male occupies himself meanwhile with the digging

work and has soon disappeared in the soil. An approaching female (yellow) is treated less

peacefully. Scarcely had it shown its identity through its scent as such, than it was attacked

savagely, and was driven away after a strong fight. The bright green female did not come offany differently. From this the white maintained its place. During the watch the guarding

animal stayed directly in the soil. I sat the yellow, already once expelled female, with forceps

on the mole. Then it had plenty of time to work, and was mated with the bright blue male. By

accident the white female came into its vicinity, the fight was repeated, then again the yellow

animal left. Now it was no longer possible, to bring the defeated female onto the mole and for

it to remain there. I tried it so often, but these animals were good at escaping from these

places. The strong female even set back the yellow, and then also attacked it, when I held it

tightly with the forceps. Both layed into one another so quickly, that I was able to lift both

fighters together without them separating. During these maneuvers a newly arrived male

(white) succeeded in getting under the body unnoticed by the white female.

We see how well a female fared in the field of other females! How do the males behave

among one another? The two worked during the whole duration of the experiment on the


14/37

same carcass without mutually disturbing each other; the mole is sunk further into the soil

through their common vehicles. Finally even a third male arrived. Suddenly, a loud chirping

becomes audible and in a wild chase 2 males appear under the carrion, the third (white) close

behind them. This comes (as in the females) at last usually to a fight, from which the white

male comes off victorious and turns back to this work, while the fugitives appear to keep

away from the mole now. After a further hour in which nothing more in particular happens

and the mole is rapidly fully covered with soil, the observations were discontinued. On the

following morning by digging it up, I found on the carrion the white pair alone, whose

isolation had taken place in the described way.

If the described events are valid as typical, then they also show certain peculiarities. For

example, the sort and manner as the victorious female creates an ambush in the form of a

subterranean passage, do not describe the rule, although this was also observed in other

females now and again. Frequently the female briefly undertook trips radiating out from the

carrion but always returning to the body. I would like to interpret this behavior of the female

as a species watch (guard) service, during this the close vicinity of possessions at risk is

searched for strange females and prevents an unnoticed intruder going by. Further the

experiment demonstrates that the second female was superior to all remaining in strength anddrive to attack. If this were not the case, then the carrion could be conquered still by the third

or even fourth female and so several times change owners.

The experimental description has shown in which way the fight between grave diggers of the

same sex brings about the peculiarity of a single pair from a large number of individuals. It is

true that the described mechanism is not absolutely clear, but still works with greater certainty

except with a very small number of exceptions (4 out of 254 cases) in which two females

were found on one and themselves buried the carrion.

But how is it, that 53 times only females were found. So far it is not a matter of cases in

which a female mated elsewhere had layed out the burrow; this is the result of one female

changing instinct after completing the passage digging. The female that puts up with adigging male, however, attacks after completion of the crypt of the partner and drives him

away. Most of the females enter the change in behavior shortly after egg laying, yet can

before; after this time the male can be expelled from the brood chamber. Under these

circumstances, different sexes of the same species of grave diggers alone fight. I was never

able to observe, under the same conditions, fighting between different sexes of individuals in

N. vespilloides.

The fighting instinct of males and females has a certain distinction. The female behaves

during the time of passage digging in a vigilant, and limiting manner and neglects the digging

work more or less. The male however turns exclusively to the work. First if they by chance

meet at their work, the fighting instinct is aroused. Then their fight does not differ from that

of the female.

The circumstance that temporarily several males are able to be found digging at once on the

same carcass, is naturally very conspicuous in the biology and has given occasion to far-

reaching, theoretical remarks. One remark by Fabre says that the researcher saw, on average,

more males to use the help of pairs, often also the effect of social instinct. "Un couple etait-il

dans l'embarras, avertus par le fumet, des aides surviennent, servants des dames, qui se

glissent sons la piece, la travaillent de l'echine et de la patte, l'enterrent, puis s'en vont en

laisent a leurs joies les maitres de caens". Quite similarly Renkev (1913) interpreted this

appearance as "the first germ of an altruistic instinct", while Schroder (1929) in his even

wanted to recognize a " particular case of the use of strange foreign expediency".

Alverdes (1925) expressed the presumption the opposite way, that the assembly of several

grave diggers at carrion suitable for broodcare showed only "association", in a sociological


15/37

respect, whose origin lead back to environmental factors, not the existence of social instincts.

This explanation neglects the crucial point of the problem, namely the question of what

causes the surplus individuals to leave the carrion. So far, however, only the carrion work of

the males from my results confirms Alverdes' prediction.

For inspite of the common work which in truth is only based on the chance adding up of

single results, in fact no relationship exists between the digging males. Every male works for

himself alone and for himself personally. His advantage lies in the chance to reproduce

successfully and this possibility is never abandoned without a fight in favor of a competitor.

Every male looses much more than every female, first then his place and if it is forced to do

that by a mate of the same sex, which is superior to him in strength and skill. Through this

therefore, the prediction of Renkers' (1913), as also the explanation of Schroder's 1929, is

without foundation.

c. Ecology of the fight.

The main value of the fight between gravediggers of the same sex is frequently that a single

pair remains behind at the carrion and their descendants find sufficient food. The existence ofthe instinct to fight is already sufficiently motivated through this.

But it appears to me that this fighting still raises a further use: An effective choice within the

species. This opposes us more clearly in the fights of females. Any female which is in

possession of a body has to prove, as it were, before a new approaching female by way of a

fight its strength, skill and the normal functioning of certain instincts. Then the carrion passes

into possession of the superior animal and so that the possibility of egg laying on the piece of

carrion in question remains only for the better equipped female, and obviously encourages the

propagation of the stronger and healthier female. While one is allowed to accept that this

stronger selection puts the reproduction of weaker or even genotypically retarded females in

question.

The translation of these results in the fighting of males with one another however meets with

difficulties. While with the driving away of female animals also these germ-cells become

distant, when any female first proceeds to egg-laying after the burying of the carrion and these

long winded preparations, the numerous males are chased away often first because of the

small desire to fight off male animals after they have already mated with healthy females of

the same carrion. In such cases their violent removal becomes meaningless as a means of

eliminating inferior quality. A cause of selection, through fighting, therefore can be found in

the males only in one case, in which the chased male did not succeed in mating. The possible

drawback in this for the species made up for through the gain would result from the adding up

the work performance of present male at the same time.

This remark "natural breeding choice", which is recognized in the fighting betweengravediggers of the same sex appears suitable from consideration to permit a classification in

the narrower conception of "sexual breeding choice". Although those fights, at least by the

females, determine the permission of participation of individuals in reproduction, nevertheless

the lack of connection of fighting animals to the representatives of the different sexes

excludes the sexual breeding choice. The fighting of gravediggers is for possession of the

carrion, not for possession of females, and males respectively. Any Necrophorus fights only

in the direct vicinity of a suitable body for the broodcare. At meetings of the sexes under other

conditions, for example of large carcasses, mating pairs are frequently found without

observations of hostile attitudes or fights between individuals of the same sex.


16/37

d. Fight with strange species or races of gravedigger

Gravediggers are sometimes also ready to defend the stores of food committed to the brood

against representatives of strange Necrophorus species. Naturally it gives in easily for in

districts with mixed environmental characters several species are attracted to a carcass. Yet

fights do not always result from this meeting; the weaker species usually hastily retreats

before interacting with a larger species. This is established particularly frequently in N.

vespillo and N. humator. A N. vespillo female leaves the prey it has fiercely defended against

females of its own species, when approached by N. humator of either sex. Even strong N.

vespillo females, which in size are scarcely smaller than weak example of N. humator, retreat,

leaving the carrion to a N. humator. Occasionally particularly aggressive individuals of N.

vespillo fight against an enemy of a strange species with variable results, as I observed in

eight cases. The fight developed then as between the same species, however it went ahead

independent of the sex of the two participants. More males and females attack representatives

of the weaker species, for example N. vespillo or N. vespilloides, without any hesitation

provided that these do not avoid the attack through hurried escape.

A remarkable observation is inserted here. In the surroundings of Frankfurt the species, N.vespilloides shows considerable variation concerning elytral markings. The black crossband

which normally goes through the elytra unbroken, slightly behind the middle and often

extends so far that the distally lying red yellow crossband, is reduced to two almost round

spots, is displaced and in several examples is so strongly reduced that only a row of small

black dots or a long line remains between which both red yellow marks come together. There

the existing various different kinds of elytral marking show all transitions, missing any

possibility which separates stronglv differing forms with the help of named characteristics as

hereditary race of the species N. vespilloides

The investigation offered me the opportunity to establish whether really only one pair from a

large number remained behind on a buried carcass. I observed that females with strong elytral

markings either always paired alone or with a male differing from the norm by the samedegree. This observation is based on twelve recorded cases which were all positive. I never

observed a negative case, and I can rely on several more positive but not recorded

observations. If one considers the relative scarcity of this extreme observation, it appears that

it could not be due to chance; one explanation is that the abnormally marked females fight or

drive away the normal males and only leave males similar to themselves unmolested. This

supposition assumes a physiological difference of those females from the normal which can

only be based on hereditary mutation. Then would mention the possibility for it that the

weaker differences of all degree is considered genotypical without being isolated

physiologically from the stem type. The extremely different form had the value of a beginning

species.

e. Course of the fight

After establishing which individuals fight each other we now move towards the kind of fight.

The typical fight of a gravedigger happens with such speed that it is impossible at the first

observation to grasp in this confusion fast moving legs of individual actions. Repeated

observations of the incident supported by instantaneous photographs finally allowed

recognition of the real stages of the fight. How quickly the movements were carried out

comes from special difficulty of the photographic technique. At first, when the exposure time

was reduced to under 1/100 sec the picture received sharp contours. Most were therefore

taken with an explosive of 1/250 sec. I operated with "Agfa instant flashes." It offers the

advantage that at the moment of the brightest illumination which lasts for the duration of

1/250 sec., the adjusted shutter of the camera was released electronically. The duration of the

fight amounted to the quickness of movement corresponding to a few seconds. Only rarely for

example with very fatigued animals did it take a longer time.


17/37

The beetles usually simultaneously came upon the lip of the abdomen of others scent, began

the fight in opposite positions. Next the opponent throws himself at the side and seizes the

opposite side of the head and thorax. In this attitude one sees how each of the fighters works

the abdomen of the adversary with its mandibles. The closed jaws slide repeatedly from distal

to proximal part and bite, where they push off the hindrance as at times on the segmental

boundary. To this point the fight still remains undecided. Soon the firm hold of the beetles

appears to loosen. Each individual tries to move his adversary with his legs, for this the

longitudinal axis is put across its own. If one of the fighters succeeds in this, the fight is soon

decided. The beetle which at first squeezes his opponent with his legs, now has an easy

match. He presses his victim together many times with such strength that one hears the chitin

cracking. The animal which is stuck under the firm grip of the legs in a living vice is unable to

offer resistance while the limbs are shackled to him. Fig. 5 shows this phase of the fight with

which its end is reached. Again free, the defeated gravedigger takes to flight immediately.

The fight takes another start, if one of the escaping animals, which ought to be withdrawn or a

young beetle appeases his hunger on the carrion intended for the brood. In both cases the

persecutor tries to seize with his forelegs from behind the last or second last pair of hisopponents and these pulled close with a jerk. Here the animals soon lie against one another on

their sides. In contrast to the above situation they have an equal tendency to be righted as Fig.

6b illustrates. The rest of its course follows as described above.

Finally still the result of the fight remains to be considered from the individual concerned.

The weapons of the gravediggers which are employed in the fight are above all the legs, in

particular the last pair, the mandibles being of secondary importance. Although the fight

advances on strength and wildness one hears at times loud cracking of the chitin. I have never

seen a beetle emerging hurt from it. Conspicuously indeed the comparatively high percentage

of mutilated individuals remains, which one comes across at the time of reproduction. Mostly

it concerns missing tarsi, sometimes also missing tibiae or antennae. It is also possible that

these animals have lost these parts of the body through their difficult digging work; Inevertheless incline towards the assumption that also during the fight, injuries can originate.

On the one hand, the observations speak for this interpretation for I repeatedly found injured

individuals full ovaries with mature eggs. This suggests that the animals in question probably

still had not even dug. Also, the mutilated animals are particularly aggressive; they are more

frequently willing to fight the others, especially strange species and perhaps stronger

individuals.

A recurring effect of fighting is the speedy escape of the weaker animal which as result of

receiving attraction a clear change of behavior can be observed. The digging instinct which

rules the beetle up to his defeat, becomes displaced by the flight instinct. In by far the

majority of cases the escaping beetles collected in the nearest vicinity in the earth without

venturing a new attack during the following hours. On the contrary one sees them eitherclearly avoiding the body or in their search for a hiding place not giving it more consideration

than an indifferent hindrance. Still, the duration of this happening appears to be dependent on

the intensity of the sustained defeat.

Undoubtedly the escape instinct supports, so far as it concerns fights between individuals of

the same species, the fighting instinct with regard to its biological significance in most

favorable ways. Then firstly from the cooperation both results in every advantage for the

species which were already reviewed in the last chapter.


18/37

f. Relations between partners of the pairs.

That the relationships between male and female during digging are extremely loose has

already been said. The fight between beetles of the same sex round the carrion can in effect

bring about a change in the pair without releasing a visible reaction to the fight by the

indifferent remaining partner . Only the presence of the body holds both sexes together at this

time. If the carrion is removed the animals then leave the digging place and furthermore take

no notice of one another.

Nevertheless, the following observation allows one to assume an association between male

and female: the distinctly audible chirping that the male as well as the female produces with

the help of shell organs--most irregularly--arouses an impression now and then, that as if the

partners mutually answer one another. In most cases the chirping proceeds in the way that the

verse of the animal which is composed of several shrill noises of the same kind start the verse

of the partner; schematically it can be represented in the following way at which the number

of the quoted shrill noises added is of no importance:

Male ------------------------

Female -------------------------

While this incident in the male is already over after several seconds and repeated first after a

considerable length of time, I was able in three cases which were observed completely in the

wild, to overhear the loud utterances of the gravediggers which really differ from the first type

described. It is a matter of a continuous common chirping of males and females which lasts

minutes long and sounds very strange. The unusual sound picture arises that each alternates a

chirp of one animal with that of the other, schematically expressed:

Male - - - - - - - - - - - -

Female - - - - - - - - - - - - -

Whether a firm task falls to the chirping of the gravedigger at the digging and which it is, I

cannot say with certainty. In all probability the partners influence (perziperen) their mutual

chirping in some way. Copulation took place regularly in the course of digging, suggesting

that the mutual chirping is an expression of sexual excitement. Moreover the possibility exists

that the chirping operates as a warning noise and serves to frighten away related species or

genera. The common minutes-long chirping of males and females especially give this

impression. It was strengthened owing to a pair chirping in this way being constantly in

regular activity: while the male digs one frequently sees the female radiating from the prey,

going out investigating.

As soon as the digging work is thriving over the first start, the mating happens above ground.

The male climbs the female in a manner that in normal important relations his foretarsi get a

grip of the corners of the shoulders of the female and the middle tarsi grip round roughly the

epipleurons. During the actual union of both beetles the male performs a brushing movement

with his foretarsi which appears broadening in relation to the female. At the end of 3-4

seconds copulation is terminated. That same pair can however still proceed to renewed mating

before the conclusion of the digging work.


19/37

2. Relations of the beetles to their offspring.

a) Brood care

Examination of the food selected for the brood. As the gravediggers are not choosy

concerning their own food, they are also satisfied with any carrion for the provision of the

brood. Indeed the size sets the upper and lower limit. Beetles are not able to bury large pieces

and small ones do not supply a sufficient quantity of food for the numerous hungry larvae.

However, between those there remains considerable latitude. If we disregard the strongest

member of the genus, N. germanicus (this species is rare in the surroundings of Frankfurt and

so therefore too small for experimentation) carrion from the size of three day old kittens to

pieces of meat 1 cc were buried. They were usually distributed such that N. humator naturally

found the largest, N. vespilloides the smallest pieces.

Unable to detach pieces from large carrion, the beetles are directed in their care for the

offspring predominantly to the bodies of small vertebrates. When a sexually mature

gravedigger has located a carcass, he first reacts in a wholly determined way. The dead bodyis climbed, the mandibles beat here and there loosely in the carrion with the maxillary palps

clearly shaking, the antennae moving in a swinging motion. At least twice the beetle steps in

nearly vertically one upon another, standing directly on the body. Thereupon the beetle slips

under the carrion and its activity can only be guessed. He raises the prey a little from the

ground.

The single phases 1. Examination of the find with mouth parts and antennae. 2. Inspection of

length and breadth. 3. Lifting of the carrion, take place in succession, being constantly

observed before the beetle begins the real digging work. One gets the impression that the

animal deals with the act of examination of his find in this capacity. It is conceivable that

initially after the find through each constantly recurring action the chemical condition, size

and shiftability are examined, thus first from the determined combination of doses ofexcitement, the digging instinct is released. A confirmation of this presumption is seen in the

fact that a Necrophorus not once attempted bury carrion whose size exceeded his capacity.

b. Burying of a body

Naturally the direct observation of the digging activity was impaired to a large measure

because the largest part was carried out in the soil and therefore remained invisible to the

observer. This circumstance explains why the analysis of the digging technique of the burying

beetle is still outstanding. In order to be able to follow the occurrence without a break the

investigation must be completed in the wild as such under known artificial conditions. To this

end, sexually mature beetles were brought pairwise into narrow terraria to dig so that a direct

observation of the activity was possible through the glass walls.

The terraria (24 cm long, 18 cm high, 2.5 cm broad) have wood borders on the narrow side-

walls which are cut crossway square (2.5 cm x 2.5 cm). On this wood border is screwed, from

below the soil on the long side, a right angled aluminum strip. The long walls consist of glass.

Each glass plate leans on the right as well as the left woodborder so that every time

they are attached through one of the outer sides of the wood border and held by the right

angled aluminum strip underneath the glass plate on the ground is a prop. Both long walls are

held so tightly only by the metal strip that they try to slide slightly here and there as in a

rabbet. This is implicitly required in order to be able to change the glass plates during the

observation without strong shock. That often proved to be necessary against the work of the

beetle held together dirt through small soil particles or carrion. The vessel top was closed with

wire gauze.


20/37

However, under these conditions which differ strongly from the natural, some of the beetles

did not set about digging, but rather exhausted themselves through continuous attempts to

escape. In order to be able to use these animals for experimental purposes, I attempted a

further trick. A box of zinc plate was made of the size that therein holds the glass vessels put

against one another, tightly. All single cages were filled full with soil and above that still a 2

cm thick layer of earth spread out. It originated in this way a roomy surface under which the

glass terraria lay hidden. At the start the beetles were in no way confined to their work. In due

course they came across the glass wall in the soil, but this hindrance meant no more then a

stone or a hard root in the wild which the animals are able to avoid.

Actually all gravediggers went nearly immediately to the work. They fall on the way in the

depth with their prey necessarily in one of the glass boxes which then with help from the earth

surface over-topping is raised out and the observations made. The glass cage being used was

replaced immediately by another, and consequently the described experimental order is ready

for use so long as it does not lack sexually mature beetles.

If a beetle found a carrion which proved after complete examination to be suitable then thedigging work began. Next the beetle scraped more soil out from under the body. The

gravedigger thereby proceeds so that he carries soil particles from behind with forelegs which

is further given to the second pair and then reaches the last. From there the strong hind legs

shove out the mass from under the body. Though frequent repetition of the activity arises the

already mentioned small earth wall of Fabre (1899). However the dead body is not ring-like,

but only grasped round partly. Correspondingly, only a part of the carrion is also only dug

under.

More frequently than on bare, soft ground the gravedigger finds the carrion on hard leaf. This

is especially true for the the meadow-inhabiting N. vespillo. Under these conditions are

experienced the application of the already well known (Fabre 1899) ability of the beetles to

cut through grass and roots with their mandibles. If one perhaps removes the small animalbody an hour after work begins, one sees an approximately round place on which the grass

stalks are pressed on the sides and are bitten through the base so that from the small area all

sort of roots still travel through, laying free in the soil. The size of the prepared place always

is dependent on but, importantly, smaller than the object to be buried. Therefore, also in this

case the whole body is not dug under.

From this stage onwards the digging work is continued independent of the existence of a

ground covering always in the same way. Even after the

number of hindrances which it rescues from the ground in the shape of roots or small stones,

it merely fluctuates the working hours. The beetles push out more and more soil from under

the carrion and thereby deepen the already started hole without broadening it at the same time.The part of the body which is dug under begins to sink under its own weight (Fig. 8a).

Up to this time one is able to follow the work of the Necrophorus from the shaking of the

body, then suddenly this ceases and remains completely motionless for a long time. Through

that the observer receives the impression that the animal has ceased its activity, but in reality

the work goes ahead briskly and is continued in another way. The working animal has begun

from the hitherto cultivated, shallow depression to dig out a passage sloping from beneath in

the soil. There the diameter of the hole behind the original cavity falls behind with its

increasing length more and more so an automatic after sinking of the body does not come into

question (Fig. 8b). By this it appears that it is able to arrive during the work of the beetle with

no shaking of the body. As tools for the digging of the pit, the animal is served principally by

legs, which forward the soil in the already described species and manner. Now and again one

also sees the gravedigger push large lumps of soil with their neck plates.


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The newly excavated cavity reached finally a length of 3-4 cm, with very small carrion from

about 2 cm, so begin again a new phase of digging activity. The carrion now becomes forced

into the prepared hole. This represents an important achievement for the beetles. For the body

must be brought to a small volume, otherwise it does not manage to pass along the narrow

passage. The start of this working phase the beetle orients itself under the carrion so that its

back is turned towards the underground, the abdomen tip towards the newly excavated,

funnel-shaped hole. The animal now grips the body with the tarsi and hauls it in with accurate

movements of the legs from behind and like-minded movements from the head and thorax

over itself off deeper into the hole. In most cases, the gravedigger grasps the carrion in the

middle, and pulls it into the passage while the LAST SENTENCE CUT OFF WHEN

XEROXING! this way, out of it the advantage results that the carrion is pressed together in a

very much concentrated mass. This is the first step in the rounding of the body which is

experienced later in the crypt. The more the carrion squeezes itself in the slope in the cavity

leading to the funnel, the more effective the effort of the working beetles which in order are

firmly it refutes gains on the funnel wall.

How successful this working method is, is shown by a chance observation. A N. humatorfemale buried a piece of horse meat some 6-8 cm in a sunk flower pot filled to the higher edge

with earth. By aiming at the base of the vessel, the female pressed its find through holes in the

base of the flowerpot which were big enough to allow through the N. humator female a small

example. By digging up the pot, the meat was held tightly only still with a small point, while

the remaining part had already passed the narrow opening. Only with difficulty did I succeed

in pulling back the meat the same way with forceps which is able to give an idea of the

working capacity of the beetle.

Still before the carrion has arrived at the end of the prepared passage it is extended in the

beginning successful way. Fig. 8d. Scarcely does this happen round a tiny piece, so the animal

shoves itself along between carrion and soil and walks round the prey and in doing so gives it

the advantage of a smooth body shape. In this way all parts of the body become dragged herewhich still stick out of the main lump as for example tail and legs. Thereby the whole carcass

is stuck together more and more. Fig. 8e. Both activities, gradual lengthening of the passage

and hauling back the body with rounding off at the same time, alternates at length with one

another till the carrion has reached a certain depth. The thrown out material is, as already

Fabre (1899) observed, in the meantime thrown together. Only a small soil accumulation free

of plant growth betrays the activity of the gravediggers.

From the given description one presumes understandably that the carrion is not vertically

under the small hillock. Moreover, one regularly finds several centimeters laterally from the

small heap, loose earth distant in the soil (Fig Bb), an establishment, which again allows a

conclusion about the working method of the gravedigger that through digging under the prey

alone would hardly succeed in this place.

In the same way as N. vespillo goes about its work. so too does N. humator, N. germanicus,

N. investigator and N. fossor; N. vespilloides is an apparent exception. This inhabitor of drier

woods buries his finds only under mosslawns, leaf or needle litter which puts plenty of living

room at his disposal. His performance confines him thereupon to carrying the body through

the often several cm high ground covering till the carrion is put on free earth. If one finds

such a buried carcass, one can be certain to have the work of a N. vespilloides, Fig. 9. The

instinct of this species is so well adapted to the normal conditions of his environment that N.

vespilloides in a cage without ground covering is very rarely brought to reproduction as I was

able to experience with my experimental animals. However as soon as one puts plenty of

moss or needle litter in the rearing cages, they are no longer opposed to the natural course.

Thereby showing that the different phases of the digging event, which were observed in the


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work of the other species in the essentials are also the same in N. vespilloides, only on

account of the loose condition of his materials differing in appearance.

A proof that the above described manner of digging is not confined alone to the named native

species, is given in an observation of Osten-Sacken (1862). According to him, N. americanus

ought to produce a long sloping in the soil leading to a pit in which he slips in the carcass.

There this beetle ought to be instructed in the main point of snake carrion, Osten-Sacken

considered this as he believed from that of other species, differing in digging method as

adaption to the shape of prey animals. However this assumption was invalidated for other

Necrophorus species proceed independent of the shape of the body likewise. Then the

extension of the prepared hollow with increasing size of the buried object takes root, becomes

understandable if the long passages which are manufactured as a rule in N. americanus to the

taking up of snakes, is seen, while they were able to ignore decidedly shorter cavities in the

native gravediggers average for small carcasses.

The depth up to which the gravediggers bury their finds, varies with the species. In some 60

cases the distance of the soil surface vertically to the roof of the crypt was measured. Thereby

proving that N. germanicus digs the deepest. This species was only observed in captivityhowever, in which the animal moved the carrion without exception to the hottom of the cage

which was 20 cm deep; it is possible that this animal reaches greater depths in the wild. A

buried carcass of N. humator was found normally at 7.4 cm depth; the highest measured value

for this species amounted to some 13 cm. In the smaller interval from the soil surface one

finds the brood holes of the remaining species.

The time which the burying of the carcass requires is dependent on the size of the object, on

the condition of the ground of the physiologica competence and finally the number of

working beetles. The following observations which refer to a female N. vespillo give an idea.

The animal had carried a mouse in loose garden soil, with peat mixed through to a typical

depth for the species N. vespillo in 3 hours. In natural conditions in which a turf is penetrated

through, roots and stones are dealt with; this work takes up 8-10 hours in the above describednarrow glass terraria the beetles required likewise a whole night during which several long

rest pauses were observed. If several gravediggers take part in the work, so the working time

shortens in proportion to their number.

c .Rounding of the body and completion of the crypt.

One finds clumsily formed balls of carrion after the finish of the digging activity in the

ground. Fig lOa-f. show carrion taken from the crypt. From all forms shows the instinct of the

beetle to adjust the carrion as far as possible to a ball shape. The skeleton of vertebrate

animals frequently resists the rounding; from figures lOb and c this problem is obvious with a

bisected frog. Boneless pieces of meat which can be shaped anyway by the beetles keep a

perfect ball shape well. The expediency of this round form is obvious: with the smallestsurface area the ball protects the largest volume and therefore is particularly favorable to

preserve the food from desiccation.

Rounding of the carrion and building the crypt are closely connected in their origin, and arise

as a result of one and the same activity. For hours on end the beetle wanders round the buried

prey step by step in all possible ways. With its feet on the body and its back against the

surrounding earth, he lifts the mass continuously through stretching of its strong bent legs

away from itself. Through the counter pressure of the soil which opposes the back of the

beetle as well as the opposite lying side of the body, the carrion is strongly pressed together

and obtains the ball shape from the constant repeated kicking on all sides unless the strong

skeleton resists it. Necessarily through the constant pressure of the surrounding soil, a cavity

arises with hard walls in which the fully rounded animal body rests. It is the crypt. The

diameter is dependent on the size of buried object as well as that of the working beetles.


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As was recognized already by Fabre (1899), one finds the small mammal's bodies hairless, the

bodies of birds featherless also without tail or steering feathers in the crypt. How this

appearance ought to be explained, as though the results of wind decay or as the result of

active work of the beetle, Fabre left open. However, none of these possibilities alone give the

truth; first through the interlocking of both factors arise several admitted results. Through the

ungentle treatment which the body receives during the digging activities in the passages of the

narrow cavity on the one hand the sedimentary hairs or feathers which are only still loose in

the skin of the body, fall out without direct action of the beetles; on the other hand the animals

subscribe directly to their removal: after rounding the body and at the same time completing

the crypt, the beetle continues to walk round over the carrion, however with renewed activity.

Like a spatula its head now stretches with slightly open mandibles over the surface of the ball

and free the food provisions of particles for the larvae and also still attached hair or feathers.

For hours on end, only broken by short rest pauses, one sees the beetle performing these

movements which are brought about through bending in of the initial thrusting out of the

head. In this way every square millimeter is cleared stepwise--apart from direct observations--

as is recognized from an enormous quantity of tiny points which were left behind by the

mandibles in the soft substrate and which by now cover the whole carrion ball. The fallingaway--be it hairs or feathers--gather on the base of the hole and there become pressed against

the walls of the brood rooms by the gravedigger so that he covers them with a carpet similar

to the base of the crypt. This was observed at its most perfect on carrion which were buried in

soft peat, free from all hindrance. Under the conditions which in the wild are most frequent,

one finds traces of hair or of feather which have been lost for the large part already on the

way through the firm soil.

d. Egglaying

When the carrion is rounded, cleaned and resting with a smooth surface in a firm-walled crypt

(which to reach this portion of necessary activities requires in total between 12-48 hours) the

female proceeds to egglaying while the male repeats from time to time the above quotedwork.

As first Hain (1927) and V. Lengerken (1928) have stated independently the eggs of the

gravedigger are not layed on the carrion or in the carrion, but individually in the soil, as I

likewise confirmed. Unexceptionally I found in more than 100 cases, the eggs of included

species, singly in small earthholes which show a striking arrangement. They lie, as I was able

to observe in the species N. vespillo (76 cases) in some 6-10 mm intervals to both sides of a

round shaped, smooth-walled against shock, indeed little resistant passage which the mother

animal has dug from the crypt out into the soil. It is analogous to the parent gallery of the

barkbeetles, a space is quite big enough to let the female move through it unhindered. The

passage runs horizo

Documents

[Pukowski] Ecological Investigation of Necrophorus F., 1933