Forensic Entomology

Maggots and Time of Death Estimation

Entomology is the Study of Insects

Images from: www.afpmb.org/military_entomology/usarmyento/files/ArmyEntomology.ppt

Insect Biology

• Insects are the most diverse and abundant forms of life on earth.

• There are over a million described species- more than 2/3 of all known organisms

• There is more total biomass of insects than of humans. of humans.

• Insects undergo either incomplete or complete metamorphosis (Egg to larva to pupa to insect)

• Larva have a soft tubular body and look like worms. Fly species larvae are “maggots”

What is Forensic Entomology?

• Forensic Entomology is the use of the insects and other arthropods that feed on decaying remains to aid legal investigations.  – Medicolegal (criminal)– Urban (criminal and civil)

• “legal proceedings involving insects and related animals that affect manmade structures and other aspects of the human environment”

– Stored product pests (civil) 

Medicolegal Forensic Entomology

• Often focuses on violent crimes– Determination of the time (postmortem

interval or PMI) or site of human death based on identification of arthropods collected from or near corpses.

– Cases involving possible sudden death– Traffic accidents with no immediately

obvious cause– Possible criminal misuse of insects

Postmortem interval (PMI)

• Forensic Entomology is used to determine time since death (the time between death and corpse discovery)

• This is called postmortem interval or PMI).

• Other uses include• movement of the corpse• manner and cause of death• association of suspects with the death scene• detection of toxins, drugs, or even the DNA

of the victim through analysis of insect larvae.

Forensic Entomology is Applied Biology

• If it weren’t for decomposition of all living things, our world would fill up with dead bodies.

• When an animal dies, female insects will be attracted to the body. They enter exposed orifices or wounds and lay eggs or larvae.

• A forensic entomologist:– identifies the immature insects– determines the size and development of the

insects– calculates the growth of the insects and passage

through stages of the life cycle in laboratory– compares the growth against weather conditions

to estimate time of oviposition

Succession of Insects on the Corpse

• Estimates of postmortem intervals based on insects present on the remains are based on:• The time required for a given species to reach a

particular stage of development.• Comparisons of all insect species present on the remains

at the time of examination.• Ecological succession occurs as an unexploited

habitat (like a corpse) is invaded by a series of different organisms.

• The first invasion is by insect species which will alter the habitat in some form by their activities. These changes make the habitat attractive to a second wave of organisms which, in turn, alter the habitat for use by yet another organisms.

Ecology of Decomposition• Necrophages - the first species feeding on corpse

tissue. Includes rue flies (Diptera) and beetles (Coleoptera).

• Omnivores - species such as ants, wasps, and some beetles that feed on both the corpse and associated maggots. Large populations of ominvores may slow the rate of corpse’s decomposition by reducing populations of necrophagous species.

• Parasites and Predators - beetles, true flies and wasps that parasitize immature flies.

• Incidentals – pill bugs, spiders, mites, centipedes that use the corpse as an extension of their normal habitat

Image: http://www.nlm.nih.gov/visibleproofs

Decay Rates Are Variable

• Studies of decay rates of 150 human corpses at in the Anthropological Facility in Tennessee (The Body Farm)

• Most important environment factors in corpse decay: • Temperature• Access by insects• Depth of burial

• Other Factors• Chemical-- embalming agent, insecticides,

lime, etc.• Animals disrupting the corpse

Time of Death can be broadly estimated up to about 36

hoursTemperature Stiffness Time of deathTemperature Stiffness Time of deathWarm Not stiff Not dead more than three hoursWarm Not stiff Not dead more than three hours

Warm Stiff Dead between 3 to 8 hours Warm Stiff Dead between 3 to 8 hours

Cold Stiff Dead between 8 to 36 hoursCold Stiff Dead between 8 to 36 hours

Cold Not stiff Dead in more than 36 hoursCold Not stiff Dead in more than 36 hours

Differentiate between PMI and Time of Death

• These may not always equate. • Post mortem interval is restricted to

the time that the corpse or body has been exposed to an environment which would allow insect activity to begin. – Closed windows– Body in box or bag– Cold temperatures– Deeper burial

Insect species arrive at a corpse in waves like clockwork• Calculate the heat/thermal energy

(accumulated degree hour) required for each stage of the Green Bottle Fly’s life cycle.

• Possibly the greatest potential source of error in using arthropod successional patterns lies in the collection of speciments.

• Must only be done correctly to accurately sample the insects.

Image: http://www.nlm.nih.gov/visibleproofs

Calculating PMI from Accumulated Degree Hours

(ADH)From To Temp

Hours

ADH Cumulative ADH

Egg 1st Instar 70° F 23 23 x 70=1610 ADH

1610

1st Instar 2nd Instar

70 ° F 27 27 x 70=1890 ADH

1610+1890

2nd Instar

3rd Instar

70 ° F 22 22 x 70=1540 ADH

1610+1890+1540

3rd Instar

Pupa 70 ° F 130 130 x 70=

9100 ADH

1610+1890+1540+9100

Pupa Adult Fly 70 ° F 143 143 x 70=

10010 ADH

1610+1890+1540+9100+10010

Calculating ADH from Climate Data

Using the Data

• 3928 ADH in these three days (952+1488+1488).

• How many ADH of 70º are there in these 3 days?

• 3928/70=56.11 hours• 72 hours at 70º would have the

insects passing to the 3rd instar. But 72 hours at colder temperatures and insects will only be at 2nd instar stage.

Five Stages of Decomposition Fueled by Insect Activity.

• Fresh• Bloat• Decay• Post-decay• Dry (skeletal)

Fresh

• Begins at death• Flies begin to

arrive• Temperature falls

to that of the ambient temperature.

• Autolysis, the degradation of complex protein and carbohydrate molecules, occurs.

Bloat

• Swells due to gases produced by bacteria

• Temperature rise of the corpse

• Flies still present

Decay• Gases subside,

decomposition fluids seep from body.

• Bacteria and maggots break through the skin.

• Large maggot masses and extreme amounts of fluid.

• Unpleasant odor• Larvae beginning to

pupate.• Corpse reduced to

about 20% of it’s original mass.

Post-Decay

• Carcass reduced to hair, skin, and bones.

• Fly population reduced and replaced by other arthropods.

• Hide beetles are dominant in dry environments.

• Mite and predatory beetle populations increase.

Dry (Skeletal)

• Does not always occur especially if corpse is in a wet region. Maggots will stay longer and hide beetles will not appear.

• In wet environments the hide beetles are replaced with nabid and reduviid insects.

• The corpse is reduced to at least ten percent of the original mass.

• In the last stage (Skeletal Stage), only bone and hair remain.

Methods

• This project took place at the Huntington landfill beginning on September 5, 2003.

• Two different areas were chosen to deposit two pigs.

• Pig 1 was laid in a sunlit area. • Pig 2 was laid in a shaded woodland

area about 100 feet away at an elevation of approximately 20 feet.

Methods

• Both pigs were housed in cages constructed of wood and one inch chicken wire that were staked to the ground to protect from predatory animals.

• Prior to starting the project, great care was taken to prevent insect activity from taking place.

• Subsequent to death, the pigs were individually tied in two black garbage bags, placed in feed sacks, and secured.

Methods

• The pigs were kept at -80˚C in the laboratory.

• They were placed in plastic bins in order to thaw for 48 hours prior to placement at the landfill.

• Closed environment was maintained until they were deposited at the site.

Methods

• Pigs with a genetic line of a minimum of fifty percent Yorkshire.

• They were 8-10 weeks old and weighed approximately 40-50 pounds.

• Both died on July 11, 2003 approximately 12 hours apart. One died a natural death and the other was culled from the litter.

• Both of the carcasses were in very similar condition; there were no breaks, tears or cuts in the skin.

Methods

• Daily observations were made at both sites throughout the day at 7am, 1pm, 7pm, and 1am.

• Air, ground, and maggot mass temperatures were taken at each visit and observations were recorded.

• At 7am and 7pm they also collected maggot samples for analysis and photographed the scene.

• Observations were noted and samples taken for a period of nine days.

Methods

• Using insect tweezers, they collected a number of maggots and dropped the samples immediately into boiling water, to kill the bacteria in the maggots and also to straighten their bodies for easier analysis.

• The maggot samples were taken from different areas of the body in which there were large numbers present.

Methods

• The maggots were then placed into a labeled jar and preserved with 70% EtOH.

• They also collected interesting arthropods for analysis.

• All of the samples were labeled and stored for later analysis in the laboratory.

Phormia regina

Spiracles are incomplete

Third-instar larvae

Phaenicia sp

Spiracles are complete

Third-instar larvae

Results: Fresh Stage

• Flies began to arrive within minutes of pig placement however, laying of eggs was delayed 12-18 hours.

• There was already some green discoloration on Pig 2 at the beginning of the fresh stage, possibly due to the fact that it was dead about 8 hrs before Pig 1.

• 72 hrs later, the first signs of bloating occurred, ending the Fresh Stage.

Results: Bloat stage

• At about 72 hours, noticeable bloating began to occur in Pig 1.

• However, Pig 2 did not show visible signs of bloating until about 92 hours.

• The gap between the two pigs might have been even greater if they had both died at exactly the same time.

Results: Decay Stage

• Decay stage started around 102 hours. • At this point, the maggots had broken the

skin and the pigs had begun to deflate. • Decompositional fluids began to seep

from the carcass. • There was a green froth around the pig

and also a dark fluid ring around the body of Pig 1.

• Maggot activity increased tremendously, and maggot mass temperature reached its high during this stage.

Results: Post-decay Stage

• When the experiment was terminated due to the fact that maggot activity had ceased, the pigs had reached the Post-Decay Stage.

• They were mostly skin, bones, and hair, but there was some tissue remaining.

Temperature is a Factor: Pig 1

• The graph shows an elevation for maggot mass temperatures over ambient

• The fluctuation in ambient temperature induced elevated maggot activity which is consistent with other similar experiments.

Maggot Mass and Ambient Temperatures vs Time for Pig One

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Maggot MassTemperature

AmbientTemperature

Sunlit Pig

Temperature is a Factor: Pig 2

• The ambient temperature for Pig 2 was more constant because it was in a shaded area.

• The temperatures for Pig 1 fluctuated more than those of Pig 2.

Maggot Mass and Ambient Temperatures vs. Time for Pig Two

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101520253035404550

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Maggot MassTemp

Ambient Temp

Shaded Pig

Phormia Average Maggot Length vs. Time

• Shows a gradual increase then decrease for the Phormia regina

• The maggots feed and grow to a certain point when they begin to leave the carcass to find a safe place to pupate.

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Phormia regina Pig 1

Phormia regina Pig 2

Phaenicia Average Maggot Length vs. Time

• Two peaks for the Phaenicia

• Infers two generations for Pig 1.

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Phaenicia Pig 1

Phaenicia Pig 2

Two Different Maggot Generations

• These are

distinguishable by the length and obvious size difference.

• This is why we believe there are two peaks in our graph data for the Sunlit Pig.

• The photograph was taken at a time consistent with the influx at 132 hours.

Discussion

• Two different species of maggots were collected over the nine day period.

• These two species were analyzed at their third instar stages; they were able to determine the difference by comparing their spiracles.

• The third instar was the only stage that they analyzed; species determination was more evident at this stage of development.

• They also reared a sample of maggots from each pig for later species analysis.

Accumulated Degree Hours

• ADH may be calculated using temperature and hours.

• This works because there is direct correlation between temperature and maggot development.

• Our calculations were somewhat rough but relatively accurate.

ADH and Our Results

• ADH for Pig 1 was calculated as 4885.2 after nine days.

• ADH for Pig 2 was calculated as 4488.6 after nine days.

• These can be used to determine PMI for carcasses found in this area in similar conditions.

The End