Keeping sun beetles

T he sun beetle (Pachnoda marginata) is a fascinating and widely available species of fruit beetle. Sold

frequently under the guise of Pachnoda grubs, these invertebrates are often simply used as live food for reptiles and amphibians. However, sun beetles are very interesting to maintain, possessing vivid colours and a fascinating life cycle. Despite having been kept for some time now, this brightly coloured beetle’s biology is still not fully understood, offering plenty of scope for study.

In the wildSun beetles were originally sourced from areas of west and central Africa. While P. m. peregrina is easily the most common example seen in UK collections, other

Looking for a colourful, interesting and inexpensive invertebrate to keep and study? Here’s an idea from James Brereton MSc.

sun beetlesKeeping

subspecies are also available to breeders. There is a varied range

of nine recognised subspecies in total, some of which have

no patterning on the upper surface of the body.

These invertebrates occur in tropical rainforest habitats, and their diet consists of ripe

fruit. Adult beetles have a well-developed sense

of smell, and are able to navigate toward fruiting

trees. They are able to fly, which not only assists them to

reach fruit but also to track down potential mates more easily as well. In order to fly though, the beetle must first warm its body by muscle contractions - a surprising skill for a small invertebrate! Once its body temperature has reached the required level, the beetle is able to

take off and fly, albeit rather noisily and clumsily, toward its target.

Their eggs are laid on wood substrates or within the soil, and over time, the tiny white larva will start to hatch out. These larvae are humivorous, or soil-eating, and live within the leaf litter or in rotting wood until they reach sufficient size to progress to their next life stage. This will take several months. Interestingly, sun beetles have been found in some other, more unusual substrates though: Orozco & Philips (2012), for example, found P. marginata grubs developing in guano in a bat cave, which reflects their remarkable adaptability!

Much like the mealworm and other beetles, the sun beetle has a pupal phase. However, in order to protect itself during this critical phase of development, sun beetle grubs also build a cocoon – an oval-shaped cell constructed from substrates in the environment. Typically, the cocoon is made out of soil, but the

� These beetles can fly effectively, in spite of their size.

14 |Practical Reptile Keeping

FEATURE | sun beetles

� These beautiful invertebrates have been the subject of various scientific studies, but there is still much that remains to be discovered about them.

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potentially pest control organisations, are again of only limited use to breeders. Peer-reviewed information on their breeding and biology in the form of scientific papers is comparatively scarce. Studies, therefore, on enclosure use and behaviour are to be encouraged to help keepers gain a better understanding of the needs of these invertebrates.

Environmental variablesMany care sheets recommend keeping sun beetles at temperatures varying from 20-28°C (68-82°F). At present, however,

there is relatively little proven information on the ideal temperature at which to maintain these beetles. Average figures for central and West Africa, however, seem to reflect these temperature parameters. For example, information from Accra, Ghana – a region known to contain this species - shows temperatures ranging from 24-32°C (75-90°F) depending upon the time of year.

The recommended humidity level for sun beetles is around 60%, and again, this figure is also similar to data from Accra, indicating that the humidity there fluctuates from 60% to 90% year round, rising during rainy periods. It is known that humidity levels below 25% are unsuitable for sun beetles, rapidly leading to beetle mortality. To maintain a high humidity level, it is recommended that the enclosure soil is maintained in a damp state through regular spraying, to keep the soil moist, but not saturated. This is also important for the successful growth and pupation of grubs.

HousingIt is important to remember that sun beetle larvae, pupae and beetles all have different biological requirements. As such, sun beetle enclosures need to be multifunctional, in order to accommodate all life stages.

A range of enclosure types may be

cocoon may also contain chunks of wood, stone and leaf litter.

Few studies have investigated the behaviour and biology of sun beetles out in the wild, and the predominant focus for studies has been methods of controlling their numbers. Many Pachnoda species are considered pests throughout their home ranges because of the way that they attack fruit crops. These population control investigations are not really of value to those keeping and breeding sun beetles.

Studies on sun beetlesThanks to the ease of breeding and maintaining sun beetles, members of this group have been widely kept in laboratories across the globe. For scientists, the areas of key interest for study have been largely:■ The microflora (beneficial bacteria and other components) in the digestive system of Pachnoda larva.■ The microbiological structure of the body systems of adult beetles.■ The attractiveness of different chemical odours to adult beetles.

These studies, while both interesting and useful for microbiologists and

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� Minimum (blue) and maximum (red) temperatures over the course of a year, set out on a monthly basis from Accra, Ghana. Downloaded courtesy of https://weatherspark.com/ which is a great site that allows you to track climatic parameters across the globe. Provided that you know where the species that you are keeping originates, this then allows you to work out the key environmental parameters for its care.

� It is not just temperature readings that you can obtain from https://weatherspark.com/ because invaluable humidity data is also available. This shows the corresponding annual maximum (blue) and minimum humidity levels for Accra in Ghana, giving a clear guide as to what level is required by sun beetles. You can even check out cloud coverage as well on this site. Downloaded courtesy of https://weatherspark.com/

used, including the acrylic tanks normally used for stick insects. Exo Terra™ and Komodo™ enclosures can be highly suitable, but old fish tanks can also be adapted – provided that adequate ventilation is incorporated into the design. Adult beetles are unable to climb up glass or acrylic walls, but once sufficiently warm, they are capable of flying out of enclosures. A lid of some type is therefore a necessity.

SubstratesA deep substrate is a requirement for successful breeding of sun beetles. The larvae are very specialised, feeding on soil and plant matter, and studies have shown these grubs can digest highly fibrous material. They depend on an unusual digestive method known as hind gut fermentation, which means they use microbes to break down their food for them (Egert et al, 2003). In order to provide suitable foods for your grubs, create a mix of rotting wood, soil and decomposing leaves. Provided this is kept at a suitably warm temperature, your sun beetle larvae should thrive in this

� The patterning of this group of beetles, while attractive to our eyes, may help to camouflage their presence, by breaking up their body shape, and protecting them from predators.


environment.Some keepers recommend burying

fruits and vegetables into the soil for grubs to eat. Although foods of this type may be eaten, it is not necessary, as these invertebrates are fully capable of digesting leaves and wood, but as explained later, potato may be useful.

Adults will also bury themselves in the soil at night. Even if you are not intending to breed your sun beetles, provision of soil is still a requirement for good husbandry. Furthermore, if you’re keeping a colony of sun beetles together in the long term, you will need to change the soil. Remove some of the processed, digested soil – this will look like small pellets. Add in new leaf litter and rotting wood to ensure that new larvae have a constant supply of food.

Nevertheless, try to avoid disturbing

the pupal cells of the developing beetles as much as possible. These are oval-shaped objects, sometimes bored into wood or attached to furnishings in their quarters (such as the wall of the enclosure, perhaps). When you find these, place them back without delay. The pupae need warmth and minimal disturbance to develop into beetles.

FeedingThe food required by the larvae has already been covered, and pupae of course, wrapped in their cocoons, have no need for food. Adult beetles, however, unlike their larvae, have a much simpler digestive system and are unable to live off fibrous foods such as decomposing leaves. Instead, adults require the provision of fruit and vegetables in order to thrive.

� Adult sun beetles such as this Pachnoda aemula individual will bury down into the substrate at night.

� Adult sun beetles feeding on banana. Photo courtesy Evanherk.


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given lights in the enclosure, sun beetles will climb up branches and live plants in order to bask. This may be partly to increase their body temperature and activity levels. When provided with a low level (2.5%) UV (ultraviolet) light source in their quarters, sun beetles have been noted to spend long periods basking.

It is now strongly recommended to provide light for basking and increasing the activity levels of these invertebrates. If there is no light attached to your enclosure, try to place your sun beetles in a place where they will receive natural light, or light from a reptile enclosure, but

Sun beetles are equipped with an impressive ability to detect fruit odours (Stensmyr et al, 2003), and it seems that foods such as banana, melon and mango are preferred. Most fruits are taken to some extent, and there is a need to provide at least one type of fruit at all times to keep all animals well fed.

LightingSun beetles can and have been bred without any specialised provision of lighting. However, there is increasing evidence that light is important for the behaviour and welfare of this species. If

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obviously, you need to be sure that this does not impact adversely by raising the temperature and lowering the humidity within their enclosure. Never leave their quarters in front of a window in the sun – this will give them no UV benefit, because UV light is blocked by ordinary window glass.

Enclosure furnishingsIn order to bask, sun beetles need to have branches, twigs or live plants to climb. This is an important component of enclosure design. As with many invertebrate enclosures, live plants are ideally recommended, providing behavioural enrichment for your beetles.

One problem that often emerges in planted enclosures for this species is that plants often die off. The difficulty is that grubs moving through the soil may dislodge and damage the roots, while adult beetles may actively destroy the leaves and stems of the plants above ground. If the terrarium is well designed and the plants have been given time to root before beetles have been introduced, however, this may not be a significant problem, particularly if a plant light such as Jungle Dawn (Arcadia) is incorporated here. But always bear in mind that a large colony of beetles may have highly detrimental effects on any live plants in the enclosure.

One way to combat this is to incorporate fast growing plants into the enclosure. Such plants can provide both important climbing opportunities and basking areas for the beetles. A range of grasses may be suitable, but one of the most widely available plants suitable for this purpose is the humble potato (Solanum tuberosum). If planted in the soil of the enclosure, supermarket potatoes will rapidly sprout. Within roughly two weeks, these should provide stems for beetles to climb up, and also vegetable matter to supplement the diet of the larvae.

� A large number of sun beetles basking on wood in the collection at Cincinnati Zoo in the USA. Photo by Greg Hume.

� All stages in the beetle’s lifecycle (aside from the eggs) can be seen here, with a pupal casing (left), a grub (centre) and an adult beetle (right). Photo courtesy of the author.

Maintaining a colonyIf housed correctly, P. m. peregrina may breed very successfully in terrarium surroundings. Potentially, this may be useful for sourcing larval food for your amphibians and reptiles. If you are planning to keep a colony for a long period of time though, try to find enclosures large enough enabling your colony to grow. A bigger enclosure will mean that your leaf litter substrate will last longer, and grubs themselves will have better nutrition. Such enclosures will also give beetles sufficient space to move around and breed as their numbers increase.

Sun beetles can be housed with other species, and successful colonies of beetles have been kept alongside the Indian stick (Carausius morosus) and the golden-eyed stick insect (Peruphasma schultei). Some success has been achieved with a combination of sun beetles and the Madagascar hissing cockroach (Gromphadorhina portentosa) as well, providing adequate areas are given for both species to move around.

However, there are many key points about sun beetle biology that are currently not completely understood. For example, breeding behaviour, while witnessed, is not well documented, while feeding preferences and larval maturation times still need to be fully investigated. In fact, even the lifespan of adult beetles has

particular individual is still actively climbing over seven months after emerging from its pupal stage. If we don’t know how long these animals even live, what else still needs to be discovered about the biology of these invertebrates?

Other species: ■ P. m. peregrina is an excellent choice to allow you to develop experience with this group of beetles, thanks to its wide availability and the ease with which it can be bred. If you are interested in furthering your beetle collection however, a range of other brightly coloured choices exist, which can be obtained from specialist invertebrate suppliers. These include:■ Golden sun beetle (Pachnoda marginata aurantia): this related subspecies is considerably rarer in the hobby than P. m. peregrina, and it possesses a beautiful golden brown colouration.■ Garden fruit chafer (Pachnoda sinuata): a smaller species, displaying vivid yellow and black markings. Easily available to purchase.■ Metallic fruit beetle (Coelorrhina hornimani): this species has a shiny, metallic wing case, and males are unusual in possessing a horn.■ Purple jewel beetle (Smagdethnes africana oertzeni): a small yet stunning purple species, which lives up to its name in an enclosure.

This list is by no means exhaustive though, and simply serves only to confirm the variety of other species that are available for beetle enthusiasts.


not been accurately determined.

LifespanMany care sheets suggest the lifespan of adult beetles, from emergence for their pupa to death, can be anywhere from three to a maximum of five months. However, in a current ongoing study in which sun beetles have been given individual identification marks, some beetles have displayed surprisingly long lifespans, calling these figures into question. Several beetles have reached an age of over six months, and one

Did you

Male and female sun beetles can be sexed very easily. Male beetles possess a thin line running centrally down the underside of their abdomen. In contrast, females have no line here.

know?

� You can keep these beetles in the company of other invertebrates, such as the Indian stick insect, provided the design of the enclosure caters adequately for both species.

� An adult beetle in an enclosure with sprouting Crassula leaves. These succulents are very easy to grow and shallow-rooted, so they are less likely to be affected by the burrowing grubs. Photo courtesy of the author.


Further

■ Brereton, J. (2014). Sun beetle husbandry data sheet. ABWAK husbandry guidelines. Retrieved from www.abwak.com.■ Egert, M., Wagner, B., Lemke, T., Brune, A., & Friedrich, M. W. (2003). Microbial community structure in midgut and hindgut of the humus-feeding larva of Pachnoda ephippiata (Coleoptera: Scarabaeidae). Applied and Environmental Microbiology, 69(11), 6659-6668.■ Orozco, J., & Philips, T. K. (2012). Pachnoda marginata (Drury) (Coleoptera: Scarabaeidae: Cetoniinae) Developing in Bat Guano in a West African Cave. The Coleopterists Bulletin, 66(4), 378-379.■ Stensmyr, M. C., Larsson, M. C., Bice, S., & Hansson, B. S. (2001). Detection of fruit-and flower-emitted volatiles by olfactory receptor neurons in the polyphagous fruit chafer Pachnoda marginata (Coleoptera: Cetoniinae). Journal of Comparative Physiology A, 187(7), 509-519.■ Weatherspark. (2016). Average weather for Accra, Ghana. Weatherspark. Retrieved from https://weatherspark.com/averages/28541/Accra-Greater-Accra-Ghana.

reading

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In summaryThe sun beetle is very easy to acquire from many live food suppliers and pet shops. This particular beetle is both rewarding and easy to breed and yet despite its popularity, the sun beetle has been rather overlooked in terms of research. There is a large amount of information that still needs to be determined about the behaviour and biology of this invertebrate. If you are interested in studying species that you keep, it certainly presents some exciting opportunities for further research. ✥

� The lifespan of the adult beetles may be longer than thought, according to an on-going study.

The stunning metallic flower beetle.

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Keeping sun beetles