Opening Dors

My current dayjob mostly revolves around identifying and counting dung beetles. When Europeans settled Australia, they brought their farm animals with them. Unfortunately, the large piles of dung produced by cattle and horses proved rather daunting to native scavengers used to the more compact droppings of kangaroos and possums. And if you've ever experienced an Australian summer, you'll know that flies are definitely a thing. To help with this situation, Australia has had a long-running programme introducing exotic dung beetles that are better able to clean up after livestock. Most of these are members of the typical dung beetle family Scarabaeidae but one species, Geotrupes spiniger, represents a different subgroup of the superfamily Scarabaeoidea. These are the earth-boring dung beetles or dor beetles of the Geotrupidae.

Dor beetle Geotrupes spiniger, copyright Udo Schmidt.
The geotrupids are medium-sized to very large beetles, ranging in size from half a centimetre to 4.5 cm in length (Jameson 2002). Like many other members of the Scarabaeoidea, they have broad fore legs used for digging. Their short, eleven-segmented antennae end in the asymmetrical club typical of scarabaeoids but they may be distinguished from other families in that the basal segment of the three-segmented club is expanded to form a 'cup' against which the other segments may be tightly closed. The body of geotrupids is strongly convex, and is smooth and shiny dorsally but hairy underneath. In many species, the males may bear elaborate horns and/or processes on the head and pronotum.

Male Taurocerastes patagonicus, copyright Nicolás Lavandero.

Despite their size, geotrupids are secretive animals, spending most of their time in burrows underground (which may be up to three metres in depth) and usually only emerging at night. Various species feed on animal dung or decaying matter; some feed on subterranean fungi. In at least some species, eggs are laid in brood chambers within the parent's home burrow and multiple life stages may share a single burrow. Burrows may also be shared between multiple adults when conditions demand. Though adults do not directly tend to larvae, they may stock brood chambers with food supplies. In some Australian species of the subfamily Bolboceratinae, females lay a single gigantic egg at a time that may be up to 56% the size of its layer (Houston 2011). Larvae hatching from such an egg are able to develop right through to maturity without feeding.

Adult geotrupids produce a stridulating noise when disturbed which is the origin of the alternate vernacular name of "dor beetle" ("dor" being an old word for a buzzing insect). Larvae may or may not be capable of stridulation, depending on the species.

Male Blackburnium rhinoceros, copyright Edward Bell.

The classification of geotrupids is the subject of ongoing investigation. A recent classification divides the family between three subfamilies, the widespread Geotrupinae and Bolboceratinae and the South American Taurocerastinae. Morphological differences between these subfamilies, particularly at the larval stage, have lead some researchers to question whether the Geotrupidae in the broad sense represents a monophyletic group. Molecular analyses thus far seem ambiguous; an analysis by McKenna et al. (2015) placed geotrupids as part of a polytomy near the base of the scarabaeoids. As an aside, my supervisor recently asked myself and a retired colleague whether Geotrupes spiniger was the only species of geotrupid found in Australia. I replied "yes", our colleague responded "no". Our conflict, of course, was based on whether Australia's wide diversity of Bolboceratinae contributed to the count.

REFERENCES

Houston, T. F. 2011. Egg gigantism in some Australian earth-borer beetles (Coleoptera: Geotrupidae: Bolboceratinae) and its apparent association with reduction or elimination of larval feeding. Australian Journal of Entomology 50: 164–173.

Jameson, M. L. 2002. Geotrupidae Latreille 1802. In: Arnett, R. H., Jr, M. C. Thomas, P. E. Skelley & J. H. Frank (eds) American Beetles vol. 2. Polyphaga: Scarabaeoidea through Curculionoidea pp. 23–27. CRC Press.

McKenna, D. D., B. D. Farrell, M. S. Caterino, C. W. Farnum, D. C. Hawks, D. R. Maddison, A. E. Seago, A. E. Z. Short, A. F. Newton & M. K. Thayer. 2015. Phylogeny and evolution of Staphyliniformia and Scarabaeiformia: forest litter as a stepping stone for diversification of nonphytophagous beetles. Systematic Entomology 40: 35–60.

The Barrington Tops Stag Beetle

The stag beetles of the Lucanidae are among the most dramatic of all beetles. They are large, glossy, and the adult males often have greatly enlarged mandibles that are used in conflict with other males. As larvae, lucanids are found feeding on rotting wood; adults may feed on nectar and are largely nocturnal. Australia is home to its share of lucanid diversity though the need for suitable food for larvae means that they are mostly restricted to damper regions of the country. As a result, many Australian stag beetles have limited ranges, rendering them vulnerable if not (in this time of rising temperatures and reduced rainfalls) actively endangered. One such species is the Barrington stag beetle Lissapterus tetrops.

Female (left) and major male Lissapterus tetrops, from Coleptera7777.

The Barrington Tops is a mountain range forming part of the Great Dividing Range in New South Wales, direct north from Newcastle. The Barrington stag beetle was described from this range in 1916 by Arthur Lea, one of Australia's most prolific coleopterologists, and is restricted to rain forests at the upper heights of the range. Lissapterus is an endemic Australian genus of flightless stag beetles distinguished from other members of the family by the shape of the antennae. The terminal club that is usually characteristic of the antennae of stag beetles is less defined in Lissapterus with the last few segments of the short antennae being little larger than the rest. Like most other species in the genus, L. tetrops is almost entirely black, only becoming slightly reddish on the legs and antennae. It grows about an inch in length, males and females being not that dissimilar in size. Lissapterus tetrops differs from other species in the genus in lacking foveae on the pronotum and (mostly) on the head, being relatively sparsely punctate dorsally, and having the eye completely divided by a canthus. Major males have long curved mandibles with a pair of teeth internally near the midpoint, placed one above the other. Minor males and females have much smaller, more ordinary looking mandibles.

The natural history of this species is little known but it presumably resembles that of other species in the genus. Adults are found under rotting logs partially buried in the forest floor that provide food for the larvae. Adults may live for a long time, potentially up to about a year, though it is unclear what exactly they feed on. Other species of Lissapterus are mostly found in disjunct locations up and down the Great Dividing Range, their populations presumably becoming separated as the warming and drying of Australia's climate as it moved northwards forced them out of the lowlands. As the climate continues to become warmer and drier, these beetles may find themselves having to retreat higher and higher, and eventually they may find themselves with no further to go.

REFERENCE

Lea, A. M. 1916. Notes on some miscellaneous Coleoptera, with descriptions of new species. Part II. Transactions of the Royal Society of South Australia 40: 272–436, pls 32–39.

Colpochila: The Chafing of a Mega-genus

Just a few weeks ago, I discussed the melolonthines, a hyperdiverse group of beetles including the chafers that have historically presented something of a taxonomic challenge. In the comments on that post, Adam Yates brought up one aspect of the difficulties presented by this group that I hadn't gotten around to discussing. This is the presence among melolonthines of a number of what may be called 'mega-genera', large genera containing literally hundreds of species that defy attempts to break them down into more manageable units. So on that note, it's only appropriate that I move on to an example of one of these mega-genera, Colpochila.

Colpochila obesa, from Insects of Tasmania.

Colpochila is an Australian genus of melolonthines belonging to a group currently recognised as the tribe Liparetrini (Britton 1986) though readers of the earlier post may recall that relationships between Australian melolonthines and taxa elsewhere in the world remains something of an open question. Liparetrins are, on the whole, a fairly generalised group: characters of the group include a lack of metallic coloration, a labrum which sits underneath and is not fused to the clypeus, simple claws, and relatively broad hind tibiae that end in a pair of widely separated spurs that are placed one above and one below so that the tarsus when moved from side to side can move between the spurs. The two largest genera in the tribe, by a significant margin, are Colpochila and Liparetrus. Somewhere in the region of 130 species are currently recognised in Colpochila whereas Liparetrus is even more diverse. However, both genera were referred to by Britton (1986) as 'polythetic': that is, both represent assemblages of species that, while clearly connected to each other overall, are difficult to characterise from a diagnostic perspective. Species of the genus possess enough features in common that we can readily recognise them as related but it is difficult to drill down on any individual feature or set of features that is shared between all species without exception. Similarly, while I can say from experience that it is generally easy to tell at a glance whether a given species is a Colpochila or a Liparetrus, it is a lot harder to actually define what separates the two genera. The most obvious distinction is size: Colpochila species are relatively large chafers, over a centimetre in length, whereas Liparetrus are smaller. Other features that each separate most Colpochila species from most (though not all) Liparetrus are circular eyes (most Liparetrus have eyes with flattened edges in back so the eye is closer to semi-circular), antennae with more segments in the terminal club, longer elytra that leave less of the end of the abdomen exposed, and hind coxae without the translucent margins found in many Liparetrus.

The lifestyles of Colpochila species are still not very well known. As with other melolonthines, most of the life is spent underground with mature adults only emerging very briefly to breed. The active adults fly at night and may be attracted to lights; it seems unclear whether they feed at maturity. This genus is mostly found in drier habitats such as open woodland, grasslands or semi-desert (mind you, this is Australia we're talking about; drier habitats are 90% of what's going). Of the known species, over half are found in Western Australia.

A second Colpochila species, from Friends of Queens Park Bushland.

So why are Colpochila and other melolonthine mega-genera so diverse? It should be noted that straight geographical and/or ecological divergence does not appear to be the reason: not only is it possible to find multiple species of a single genus in one location but one may even collect very similar species together. It might be that the diversity of the mega-genera is artefactual, a reflection of the failure of taxonomists to properly identify relationships: any study that wanted to explain their diversity would have to study their phylogenetic relationships with related smaller genera to confirm their evolutionary coherence and/or age of divergence. However, if the current generic classification of melolonthines reflects a real evolutionary pattern, a potential explanation was proposed by Britton (1986). Adult melolonthines do not emerge immediately upon maturing but remain dormant underground awaiting a suitable environmental signal such as rainfall. However, rainfall in the arid zone at any one time is often uneven. Dormant beetles at one spot may feel the urge to emerge while others nearby may be left to wait for the next shower. The first wave will have died off before the second wave emerges, and their offspring will not yet be mature. As a result, sub-populations in a single region may become temporally staggered allowing the possibility of divergence via genetic drift. Eventually, their emergence times may drift back into sync but by then they may no longer be able to breed successfully. Could this be the reason why so many species may be found in a single location or may other factors be more significant?

REFERENCE

Britton, E. B. 1986. A revision of the Australian chafers (Coleoptera: Scarabaeidae: Melolonthinae) vol. 4. Tribe Liparetrini: genus Colpochila. Australian Journal of Zoology, Supplementary Series 118: 1–135.

The Melolonthinae: Chafers and June Bugs

Within the bewildering array that is beetle diversity, one of the more readily recognisable groups is the Scarabaeoidea, the assemblage that includes dung beetles (which, as it happens, are what I currently spend most of my days looking at) and related forms. Members of this group are easily distinguished from other beetles by their distinctive antennae, ending in an asymmetrical club with segments extending to one side like a set of fingers. Several families, many of them further subdivided into subfamilies, are currently recognised within the scarabaeoids. One of the most commonly encountered scarabaeoid subgroups is the subfamily Melolonthinae, commonly known as the chafers.

Green scarab beetles Diphucephala sp., a common genus of day-flying melolonthines here in Australia, copyright Boobook48.

Somewhere in the region of eleven thousand species around the world have been assigned to this grouping; as always, doubtless many more could be recognised by those who take the time. Melolonthinae is generally recognised as a subfamily of the family Scarabaeidae, sharing with other scarabaeids features such an antennal club in which the segments are relatively narrow and can be smoothly pressed against each other, and an exposed pygidium (the last dorsal plate on the abdomen, forming what you might think of as the 'butt plate'). Some authors have recognised melolonthines as a distinct family but this is the less commonly utilised option. Melolonthines belong to a group of mostly plant-feeding subfamilies in which the row of abdominal spiracles bends downwards towards the rear so at least the last pair remains visible when the elytra are closed. Within this cluster, melolonthines tend to be characterised more by lacking the features of the other subfamilies than by distinctive features of their own (more on that in a moment) but general features include mandibles that are not visible when looking down on the top of the head, fore coxae that do not protrude much ventrally, equal claws on each leg (at least on the mid and hind legs) and only one visible spiracle when the elytra are closed. The labrum (the piece at the front of the mouthparts that might be thought of as the insect's top lip) is usually hardened and may be more or less fused with the clypeus (the lower- or foremost section [depending how you look at it] of the front of the head capsule). Many melolonthines are noticeably hairy and/or dull in comparison with other scarabaeoids but others may be shiny and/or metallic in coloration.

Sugarcane white grub beetle Lepidiota stigma, copyright Bernard Dupont.

For the most part, melolonthines are plant-feeders at both larval and adult stages of the life cycle (Lawrence & Britton 1991). The greater part of the active life cycle is taken up by the larval stage which may last for many months (Britton 1957). Larvae mostly live underground, feeding on plant roots and humus. A number of species have made themselves known as significant pests in this manner because of the damage they may inflict on pastures or agricultural crops (the grass grub Costelytra zealandica comes immediately to mind as a good example of this in my native New Zealand). Pupation also occurs underground in subterranean cells and mature adults may remain dormant in these cells for some months waiting for conditions to be just right for emergence. Once they do emerge from the ground, however, the adult life span is quite brief, only lasting a few weeks or even days. Because of this brief emergence, and because their habit of waiting for specific environmental cues means that large numbers may appear seemingly all at once, many species have been awarded vernacular names that reflect their seasonality such as June bug (in the Northern Hemisphere) or Christmas beetle (in the Southern). Some species will feed on foliage as adults, some may visit flowers for pollen and nectar, other particularly short-lived species will not feed as adults at all. The majority of adult melolonthines are active at dusk or night, spending the days sheltered in secluded locations, but a number of flower-feeding species are active by day (Britton 1957).

The infamous grass grub Costelytra zealandica, illustrated by Desmond Helmore.

The classification of melolonthines can charitably be described as an absolute mess. As noted above, we can confidently say that they belong to a clade with other subfamilies of plant-feeding scarabaeids (the Cetoniinae, Rutelinae and Dynastinae) but the features setting them apart from these other subfamilies are likely to be primitive for the group. As such, it comes as little surprise that phylogenetic studies have failed to establish the Melolonthinae as monophyletic (e.g. Eberle et al. 2018; Woolley 2016). However, it seems that no-one thinks that an adequately expansive study that would allow them to be appropriately divvied up has yet been done. Matters are not helped by the absence of a well-established internal classification for melolonthines. Various distinct subgroups can be recognised and between twenty or thirty tribes have been recognised around the world. But the relationships between these tribes remain uncertain, as does the tribal position of many genera. Much of the revisionary work that has been done has been conducted at a regional level only. Thus, for instance, the tribal classification of Australian melolonthines established by Britton (1957) applies only to Australian species and the tribal distinctions Britton recognised may end up falling apart if one attempted to apply them to species from elsewhere. Not that the authors should be criticised for this situation: after all, when one is dealing with over 11,000 species, things rapidly tend to become unmanageable.

REFERENCES

Britton, E. B. 1957. A Revision of the Australian Chafers (Coleoptera: Scarabaeidae: Melolonthinae) vol. 1. British Museum (Natural History): London.

Eberle, J., G. Sabatinelli, D. Cillo, E. Bazzatto, P. Šípek, R. Sehnal, A. Bezděk, D. Král & D. Ahrens. 2018. A molecular phylogeny of chafers revisits the polyphyly of Tanyproctini (Scarabaeidae, Melolonthinae). Zoologica Scripta 48: 349–358.

Lawrence, J. F., & E. B. Britton. 1991. Coleoptera. In: CSIRO. The Insects of Australia: a textbook for students and research workers 2^nd ed. vol. 2 pp. 543–683. Melbourne University Press.

Woolley, C. 2016. The first scarabaeid beetle (Coleoptera, Scarabaeidae, Melolonthinae) described from the Mesozoic (Late-Cretaceous) of Africa. African Invertebrates 57 (1): 53–66.

Omorgus: A Beetle with a Taste for Hair

A group of Omorgus clambering over what looks like a scat, copyright Stephen Cresswell.

I still remember my first Omorgus. Pretty much as soon as I saw it in the pitfall trap, I knew that this was a different type of beetle from any I'd seen before. Large, knobbly, robust... it looked a picture of glorious ugliness. Which only made it all the more frustrating that, somewhere in the process of making it into the trap, this particular specimen appeared to have somehow lost its head. Without the ability to look it in the face, I might never know what I'd found.

It wasn't until later in the lab that I discovered my mistake: my beetle wasn't headless at all! Instead, the head was retracted back, hidden beneath the expanse of the pronotum (the dorsal shield of the first thoracic segment). And so I became acquainted with my first keratin beetle.

A similar Omorgus to the one I found, O. bachorum, to give some idea how I missed the head. Copyright Clare McLellan.

Omorgus is one of the handful of genera of keratin beetles, a group of relatives of the scarabs known as the Trogidae or Troginae (there has been some inconsistency as to whether trogids are treated as their own family or as a subfamily of the main scarab family Scarabaeidae). They have robust forelegs with large femora, and striate elytra that are often covered with tubercles and/or setae. Trogids vary in size from about half a centimetre in length up to three centimetres. They get their name of 'keratin beetles' from their unique diet: both as adults and larvae, trogids feed primarily on keratin such as animal hair. They are most commonly scavengers, feeding at animal carcasses (often arriving late in the process, taking the parts of the animal rejected as indigestible by other scavengers). However, they also feed on other animal foods such as insect larvae, eggs or guano, and some appear to be specialist associates of bird nests or animal burrows (Scholtz 1986). An Australian flightless species Omorgus rotundulus was found to have a gut full of other arthropods, particularly ants and termites, in quantities that lead to the suggestion that it might be an active predator rather than a scavenger (Houston et al. 2010).

An Omorgus chowing down on a dead lizard, copyright William Archer.

Earlier authors commonly treated all trogids as belonging to a single genus Trox, but more recent authors have recognised four or five genera in the family. Omorgus includes about 150 species (Strümpher et al. 2014) found mostly in arid regions. The most obvious feature separating Omorgus species from other trogids is that the pedicel (the second segment of the antennae) is attached to the scape (the first segment) subapically rather than apically. In all species but one, the scutellum (the little thoracic shield visible between the bases of the elytra) is hastate (shaped a bit like a spear-head, with a constricted base broadening out further down) rather than a more simple oval as in other trogids. The exception, T. batesi, is a South American species that is placed in its own subgenus Haroldomorgus. The remaining species are divided between two subgenera Omorgus sensu stricto and Afromorgus, distinguished by features of the male genitalia (Scholtz 1986). Afromorgus is found in Africa and Asia whereas the type subgenus contains the Australian and other American species.

Most trogids are fully capable of flight (many are attracted to lights at night) but, as alluded to above, a handful of species are flightless. In flightless species, the elytra become fused together into a sold carapace. The impression I get from scanning the literature is that flightlessness in trogids may not be so much a matter of conserving energy as it is of conserving water. For animals living on a dry diet in a dry habitat, such adaptations are only to be expected.

REFERENCES

Houston, T. F., J. Zhang & B. P. Hanich. 2010. Diet of the flightless trogid beetle Omorgus rotundulus (Haaf) (Coleoptera: Trogidae) in the Little Sandy Desert of Western Australia. Australian Entomologist 36 (4): 207–212.

Scholtz, C. H. 1986. Phylogeny and systematics of the Trogidae (Coleoptera: Scarabaeoidea). Systematic Entomology 11: 355–363.

Strümpher, W. P., C. L. Sole, M. H. Villet & C. H. Scholtz. 2014. Phylogeny of the family Trogidae (Coleoptera: Scarabaeoidea) inferred from mitochondrial and nuclear ribosomal DNA sequence data. Systematic Entomology 39: 548–562.

Dung Beetles

Flat-headed dung beetles Pachylomerus femoralis with a ball of the good stuff, photographed by Guido Coza.

The dung beetles of the Scarabaeini include 146 species found in Africa and Asia, classified by Forgie et al. (2006) into three genera: Pachysoma, Pachylomerus and Scarabaeus, with the last including the vast majority of species. The Scarabaeus species are perhaps the most famous of all dung beetles, renowned since ancient history when Egyptians saw a dung beetle rolling a ball of dung along the ground as a metaphor for the movement of the sun through the heavens*. Dung beetles collect their turd balls to use as food for themselves or for their larvae. Ball-rolling is not unique to the Scarabaeini as a method of transporting dung, however (it is also done by members of other dung beetle tribes), nor do all Scarabaeini species engage in ball-rolling.

*It probably does not say much for the standard of ancient Egyptian public sanitation that they were apparently so willing to believe that the ultimate source of all life on the planet was a giant mass of burning poop.

Flightless orange dung beetle Pachysoma denticolle, photographed by Alex Dreyer.

The flightless dung beetles of the genus Pachysoma, for instance, transport their food by dragging it along between their hind legs. Pachysoma species are also less choosy than other Scarabaeini, feeding not just on dung but all manner of organic detritus. They have specialisations allowing them to feed on drier food particles than other Scarabaeini, suitable for their arid habitats in southern Africa. In contrast, species of the subgenus Sceliages within Scarabaeus are the epicures of the scarabaein world: they feed entirely on dead millipedes, which they push along in front of themselves bulldozer-style (Forgie et al. 2005). Relatively few species of Scarabaeini feed by burrowing directly alongside piles of dung where they lay, but this may be done by Pachylomerus and Scarabaeus galenus (both of which may also transport food).

Individual of Sceliages transporting a millipede, photographed by Shaun Forgie.

Most Scarabaeini are active during the day, but a small number such as Scarabaeus satyrus are nocturnal in habit. In the phylogenetic analyses conducted by Forgie et al. (2005), these nocturnal species usually formed a single clade. Had the ancient Egyptians observed the nocturnal dung beetles as well, they could have presented us with a sky full of poo at all hours.

REFERENCES

Forgie, S. A., U. Kryger, P. Bloomer & C. H. Scholtz. 2006. Evolutionary relationships among the Scarabaeini (Coleoptera: Scarabaeidae) based on combined molecular and morphological data. Molecular Phylogenetics and Evolution 40: 662-678.

Forgie, S. A., T. K. Philips & C. H. Scholtz. 2005. Evolution of the Scarabaeini (Scarabaeidae: Scarabaeinae). Systematic Entomology 30: 60-96.