Philonthus: Too Many Staphylinids

Philonthus marginatus, copyright James K. Lindsey.

Working with staphylinids, it has to be said, can be horrible. They are treated as one of the most diverse of the beetle families—perhaps the most diverse of all—but compared to other diverse families they attract relatively little study. The majority of staphylinids are usually either very small or soft-bodied, not uncommonly both together, making them difficult to prepare and maintain as dry specimens. For the soft-bodied species, with their reduced elytra, many of the easily visible features that can be so useful for other beetle groups are obscure or unavailable. They also tend to be drab in coloration, without much in the way of striking patterning. As a result, it is often impossible to identify staphylinid species without examining minute features of the appendages or the genitalia. Something to keep in mind as you read the following.

Species of the genus Philonthus are relatively large as staphylinids go, often about half a centimetre in length, but they are certainly not free of the problems affecting other members of the family taxonomy-wise. The genus is massively diverse—over 1200 species have been described from around the world. Attempts have been made to break them down into more manageable chunks, such as through the recognition of subgenera, but these have mostly failed to gain much traction. Most recent authors have only recognised informal species groups within the greater mass.

Philonthus carbonarius, copyright James K. Lindsey.

In general, species of Philonthus are smooth, without excessive hairs, and have labial palps with the last segment fusiform and about as wide as the penultimate segment (Tottenham 1955; Stan 2012). Males have the aedeagus (the intromittent organ of the genitalia) rotated in the abdomen so its paramere (off-branch) is located on the left side rather than ventrally as in other genera (Tottenham 1955). Some species may have a metallic sheen to their coloration; others are a plainer black or reddish. Species may also differ in the number and arrangement of setae on the pronotum.

Where their lifestyles are known, most Philonthus are associated with decomposing organic matter such as animal dung, compost or leaf litter. Some are predators of other insects and insect larvae found in such habitats (such as fly larvae); these species have highly developed senses to locate decaying matter, and are strong fliers to disperse to suitable habitats (Majka et al. 2009). Some species of Philonthus may act as predators of other pest insects, helping to keep their numbers down.

REFERENCES

Majka, C. G., J.-P. Michaud, G. Moreau & A. Smetana. 2009. Philonthus hepaticus (Coleoptera, Staphylinidae) in eastern Canada: are distribution gaps distinctive features or collecting artifacts? ZooKeys 22: 347–354.

Stan, M. 2012. On the species of Philonthus Stephens (Coleoptera: Staphylinidae: Staphylininae: Staphylinini: Philonthina) in the collections of Romanian natural history museums. Travaux du Muséum National d'Histoire Naturelle "Grigore Antipa" 55 (2): 233–276.

Tottenham, C. E. 1955. Studies in the genus Philonthus Stephens (Coleoptera: Staphylinidae). Parts II, III, and IV. Transactions of the Royal Entomology Society of London 106 (3): 153–195.

Sunorfa

The Queensland pselaphine Sunorfa nigripes, from Chandler (2001).

When I began researching the taxon that was to be the subject of this post, I was surprised to discover that it had weaseled its way onto this site once before. Back in the day, I used an example of the beetle genus Sunorfa to illustrate a post about a closely related genus for which I had been unable to find an image (before a reader pointed me in the direction of one). Sunorfa is a member of that wonderful group of miniature gargoyles, the Pselaphinae (I had the pleasure/pain of sorting a handful of pselaphines at work just the other week; their minute size [usually only a millimetre or two long] makes them a real challenge to work with but their bizarre morphologies make it impossible to resent them). Most species of Sunorfa are found in tropical rainforest litter in southern Asia and Australasia from Sri Lanka to Fiji with the highest diversity of species in New Guinea. In addition, a handful of species are found in the Seychelles. I haven't come across any direct indication of what Sunorfa are doing in all these places but presumably, like other pselaphines, they are predators of even smaller arthropods.

Distinctive features of Sunorfa compared to other pselaphines include a strong transverse sulcus (groove) across the rear part of the pronotum, and a cylindrical abdomen in which the upper tergites and lower sternites are fused into single continuous rings. They also have characteristic foveae (deep depressions) on the top of the head, the base of the elytra including on each side at the 'shoulders', and in the middle of the metasternum (the rear underside section of the thorax) (Chandler 2001). Similar foveae are found in one form or another, in one place or another, on most pselaphines. They have received a lot of attention in taxonomic studies (their appearance and distribution is one of the most reliable features in distinguishing pselaphine taxa) but their function is less well known. Chandler (2001) expressed the opinion that foveae in different parts of the body serve different purposes. Those on the thorax have solitary, sensilla-like setae at their centres and probably represent sensory structures of some kind. Conversely, foveae on the head and abdomen lack such setae and commonly connect to one another internally to form solid tubes. These tubes may function as struts, providing the body with rigidity and strength as the animal is reduced down in size.

REFERENCE

Chandler, D. S. 2001. Biology, morphology, and systematics of the ant-like litter beetle genera of Australia (Coleoptera: Staphylinidae: Pselaphinae). Memoirs on Entomology, International 15: 1–560.

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.

Small Carrion Beetles: A Bunch of SBBs

A fairly typical small carrion beetle, Catops tristis, copyright Trevor and Dilys Pendleton.

Anyone who takes on the task of beetle identification will soon discover that (to agree with Haldane) their sheer diversity can be overwhelming. Bird-watchers often complain about the challenges of identifying what they refer to as LBJs, Little Brown Jobs, but entomologists may have as much if not more to complain about when faced with the prospect of SBBs: Small Brown Beetles. The features marking a particular SBB as one family or another are often (at least to a novice) difficult to distinguish; members of unrelated families may look remarkably similar, whereas close allies may look surprisingly different.

The Leiodidae are, for the most part, firmly in the ranks of SBBs. This taxonomically small but morphologically diverse family is hard to come up with a coherent description for: though modern coleopterists have little doubt that they form a coherent clade, certain subgroups have become notably divergent. At least one leiodid, the beaver parasite Platypsyllus castoris, barely even looks like a beetle at all and was classified for a brief period in the 1800s as a distinct order of insects. Nevertheless, most leiodids are recognised by the structure of their antennae: the five-segmented club at its end has a distinct constriction as the eight antennal segment is smaller than the seventh and ninth segments on either side. Many leiodids are scavengers of plant or animal matter, but some are fungivores and a few (as already indicated) are parasites of mammals.

Small carrion beetles of the genus Sciodrepoides feeding on a deer carcass; copyright Stephen Cresswell.

Among the various subgroups of the Leiodidae are the Cholevini, commonly known as small carrion beetles. As their name indicates, these mostly feed on the remains of dead animals, though at least some are not above scavenging on other decaying matter. Some species are found in subterranean habitats, such as caves or the burrows of rodents, feeding on guano or other refuse. The Cholevini are one of the tribes in the leiodid subfamily Cholevinae, which has sometimes been treated in the past as a separate family Cholevidae or Catopidae. The Cholevinae differ from most other leiodids in the presence of an occipital carina or crest on the back of the head; such a carina is also present in the parasitic Leptininae, which Peck (1990) speculated to be derived from the cholevines. Members of the tribe Cholevini differ from other Cholevinae in having the setae on the elytra irregularly arranged (vs arranged in rows), giving the elytra a granular rather than a striate appearance.

Members of the Cholevini are mostly found in the Holarctic region, with only a few species in the Oriental region and none further south (Peck & Cook 2002). The greatest diversity in the group is found in Eurasia; only four of the 24 genera are found in North America, and only one of these (the monotypic Catoptrichus frankenhauseri) is unique to that continent. For the most part, cholevins do not vary much in appearance, and species are difficult to distinguish without examining the genitalia (these are true SBBs). Catoptrichus frankenhauseri has distinctive antennae, with lateral projections on either side of each segment(C. frankenhauseri is also noteworthy for the manner of its initial discovery, with the type specimen being collected from a human cadaver [Peck & Cook 2002]). Some of the subterranean species of cholevins have reduced eyes or wings, and a handful of species are entirely flightless.

REFERENCES

Peck, S. B. 1990. Insecta: Coleoptera Silphidae and the associated families Agyrtidae and Leiodidae. In: Dindal, D. L. (ed.) Soil Biology Guide pp. 1113–1136. John Wiley & Sons.

Peck, S. B., & J. Cook. 2002. Systematics, distributions, and bionomics of the small carrion beetles (Coleoptera: Leiodidae: Cholevinae: Cholevini) of North America. Canadian Entomologist 134: 723–787.

The Little Tike that is Tychus

Male (left) and female of Tychus niger, copyright Lech Borowiec.

Another brief beetle post for today. The species in the image above is the type species of Tychus, a genus of about 150 species of pselaphine beetles found in Eurasia and North America. Chandler (1988) regarded the North American species as a separate genus Hesperotychus but Kurbatov & Sabella (2008) felt that the differences between species from the two continents were not enough to warrant separation. There's probably still some work to be done here.

Like many other pselaphines, most of the work on Tychus has focused on the morphology of the various species, with relatively little having been said about its life habits. Heer (1841) described the habitat of T. niger as 'sub lapidibus et in graminosis' which I believe means 'under stones and among grass', and Kurbatov & Sabella (2008) recorded collecting a specimen of Atychodea pilicollis, a related species, in damp sand. The large, broad-ended palps (the appendages on the head behind the antennae) of Tychus species suggests that they are probably micropredators, like the pselaphine Bryaxis puncticollis whose hunting behaviour was described in an earlier post. Like most pselaphines, the small size of Tychus species means that they generally escape observation.

Tychus is the largest genus in the pselaphine tribe Tychini. Tychins are most diverse in the Holarctic region, with only a very few species found in southern and south-east Asia. Chandler (1988) characterised the Tychini by the shape of the third segment of the palp, which is invariably longer than wide, and by the antennae usually being inserted close together on a narrow rostrum, though this varies a lot in distinctiveness between species. Kurbatov & Sabella (2008) also identified a number of other features representing possible synapomorphies of the Tychini, and suggested that the Oriental genera Atychodea and Amorphodea represent the sister taxon of the remaining Holarctic genera. The genera of Tychini are all fairly similar in appearance; notable distinguishing features of Tychus include an asymmetrical aedeagus (the intromittent organ in the male genitalia) and the arrangement of foveae (hollows) on the elytra and sternites. Males of Tychus often have one of the antennal segments modified as in the male of T. niger shown above, with a median segment noticeably thicker and broader than those on either side. The purpose of this enlarged segment, as with so many other features of pselaphines, seems to be unknown.

REFERENCES

Chandler, D. S. 1988. A cladistic analysis of the world genera of Tychini (Coleoptera: Pselaphidae). Transactions of the American Entomological Society 114 (2): 147-165.

Heer, O. 1841. Fauna Coleopterorum Helvetica, pars 1. Impensis Orelii, Fuesslini et Sociorum: Turici.

Kurbatov, S. A., & G. Sabella. 2008. Revision of the genus Atychodea Reitter with a consideration of the relationships in the tribe Tychini (Coleoptera, Staphylinidae, Pselaphinae). Transactions of the American Entomological Society 134 (1-2): 23-68.

All About Buris ensipes

Sunorfa, from here.

The beetle pictured just above is not the intended subject of today's post. It is a related beetle found in Thailand, but I've used its photo instead of one of today's subject because, as far as I have been able to find, today's subject has never been illustrated. It was described as Dalmodes ensipes from San Esteban in Venezuela by Raffray in 1891, before it became de rigeur to illustrate any new species described (Raffray did illustrate a number of other species described in the same paper, but not this one). It has since been recorded from Antigua and Trinidad in the West Indies by Park et al. (1976), who also indicated that it should be placed in the genus Buris instead of Dalmodes, but did not illustrate it. Park (1942) had previously placed it in the genus Bythinophysis, but did not illustrate it then either. I have not been able to find any illustration of another species of Buris. Nor have I been able to find illustrations for any other species of Dalmodes, nor of Bythinophysis. Sadly, this is not an uncommon state of affairs for insect species. I did briefly consider the idea of composing an illustration of a potential Buris ensipes on the basis of Raffray's (1891) verbal description, but then I remembered that I was a rubbish drawer.

Buris ensipes is a member of the beetle group known as the Pselaphinae, of which another genus, Bryaxis, has previously been featured on this site. Like Bryaxis, Buris ensipes would probably be found in leaf litter, or possibly within rotting wood (specific collection details for Buris ensipes have not been recorded, but Park [1942] described pselaphines as found in both habitats). Also like Bryaxis, it is probably a micropredator, though again no record of its life habits has yet been made. Buris ensipes probably looks roughly similar to the photo of Sunorfa above, but Raffrays' (1891) description indicates that it would have shorter antennae (the first segment is described as subquadrate, and the end as obtusely pointed). A curved, transverse fovea (depression) is described as present in the rear half of the pronotum, and the elytra bear a pair of subhumeral foveae (i.e. just near the 'shoulders'). The fourth abdominal segment is toothed on either side. Also distinctive is the shape of the hind tibia, which is bisinuate with a median tooth. Overall, it is just over one and a half millimetres in length.

And that, as it stands, is just about all about Buris ensipes. Like all too many organisms, we have a morphological description, a few localities, and not a heck of a lot else. Buris ensipes just needs a little more love.

Update: A big thank you to Stephen Thorpe, who managed to do what I couldn't and locate an illustration of a Buris species, B. brevicollis, in Sharp (1887). I've reproduced the figure below; it also tallies reasonably closely with Raffray's description of B. ensipes. Potential differences between the species are that Sharp makes no mention in B. brevicollis of a toothed fourth abdominal segment like that of B. ensipes (though one should always be extremely cautious of assuming a given feature to be absent simply because a given author didn't mention it), and that Raffray referred to the tibial spine of B. ensipes as 'minute' whereas that of B. brevicollis looks quite sizable.

REFERENCES

Park, O. 1942. A study in Neotropical Pselaphidae. Northwestern University Studies in the Biological Sciences and Medicine 1: i-x, 1-403, 21 pls.

Park, O., J. A. Wagner & M. W. Sanderson. 1976. Review of the pselaphid beetles of the West Indies (Coleopt., Pselaphidae). Fieldiana Zoology 68: 1-90.

Raffray, A. 1891. Voyage de M. E. Simon au Venezuela (Décembre 1887-Avril 1888). 10^e Mémoire. Psélaphides. Annales de la Société entomologique de France, ser. 6, 10: 297-330, pl. 6.

Sharp, D. 1887. Fam. Pselaphidae. In: Biologia Centrali-Americana. Insecta. Coleoptera, vol. 2, pt 1, pp. 1-46.

Bryaxis on the Prowl

Pselaphine, probably Bryaxis bulbifer, photographed by Krister Hall.

Bryaxis is a large genus, with over 400 described species and subspecies (Hlaváč 2008), of small beetles belonging to the group known as the Pselaphinae, a subgroup of the Staphylinidae. In older references, you'll see the pselaphines referred to as a separate family Pselaphidae from the staphylinids, but most authors now include it in the latter as it has become clear that the pselaphines are not only related to the staphylinids but nested well within them. It is not so surprising that this was not immediately recognised: your average staphylinid looks something like this:

Paederus riparius, from here.

Bryaxis species are mostly found living in leaf litter, where they are predators of other micro-arthropods such as springtails. If you look at the top photo, you will be see two appendages with paddle-shaped endings attached to the head just behind the antennae. These are the maxillary palps, often enlarged in pselaphines (sometimes ridiculously so). Glands on the inside of the palp 'paddle' produce a sticky secretion, and the palps are used to grab the prey when hunting. The process of prey capture in Bryaxis puncticollis was illustrated by Schomann et al. (2008):

Prey detected!

Palps at the ready...

Pounce!

The final parts of the process. The springtail is held tail-upwards so that it can't escape or injure the beetle using the forked furca, the 'spring' underneath its abdomen.

As befits a large genus, Bryaxis has a truly headache-inducing taxonomic history, summarised by Besuchet (1966). The genus was first named by Kugelann in 1794. Kugelann's work can't have been that widely publicised, however, because in 1817 Leach gave the name Bryaxis to a different genus of pselaphine. Most subsequent authors used Bryaxis in the sense of Leach, and included Kugelann's original Bryaxis in the genus Bythinus, until this was corrected by Raffray in 1904. Raffray treated Bythinus as a junior synonym of Kugelann's Bryaxis, and placed Leach's 'Bryaxis' under the name Rybaxis. Even so, some European authors persisted in using Leach's Bryaxis.

It wasn't until the 1950s and 1960s that the usage of Bryaxis became stabilised, but there was one further wrinkle to the story. When Raffray identified Bythinus as a synonym of the true Bryaxis, he separated out a few previous Bythinus species as a new genus Bolbobythus. However, one of those was the type species of Bythinus. So, as finally laid out by Besuchet (1966): what had been called 'Bolbobythus' was really Bythinus, 'Bythinus' was really Bryaxis, and 'Bryaxis' was really Rybaxis! What could be simpler?

REFERENCES

Besuchet, C. 1966. Bryaxis Kugelann, 1794 and Bythinus Leach 1817 (Insecta, Coleoptera): proposed addition to the Official List in their original sense. Bulletin of Zoological Nomenclature 23 (2-3): 114-116.

Hlaváč, P. 2008. A new cavernicolous species of the genus Bryaxis (Coleoptera: Staphylinidae: Pselaphinae) from the island of Mljet. Natura Croatica 17 (1): 1-8.

Schomann, A., K. Afflerbach & O. Betz. 2008. Predatory behaviour of some Central European pselaphine beetles (Coleoptera: Staphylinidae: Pselaphinae) with descriptions of relevant morphological features of their heads. European Journal of Entomology 105: 889-907.

The Corotocini in their Gut-Swollen Glory

Specimen of Thyreoxenus brevitibialis, photographed by Taro Eldredge.

Staphylinids are one of the most diverse groups of beetles out there, despite not looking like what most people would identify as beetles. But that's okay, because there are staphylinids that don't look much like what most people would identify as staphylinids, like the beautiful beasty in the photo above. Thyreoxenus brevitibialis is a member of the staphylinid tribe Corotocini, a distinctive grouping of termite inquilines.

Inquilines are animals that live in association with social insects such as ants, bees or termites. A number of staphylinid lineages have adopted the inquiline lifestyle; another group of termite inquilines, the Termitusina, was briefly covered in an earlier post. The Corotocini are the largest group of termite-inquiline staphylinids, living in association with termites of the pantropical subfamily Nasutitermitinae. Distinguishing features of the corotocins include fusion of the mentum and submentum (two plates on the underside of the head) and distinctive sensilla on the antennae (Seevers 1957). Most notable, however, is that all members of the Corotocini show some degree of physogastry, swelling of the abdomen*. In most species, the greatly inflated abdomen is recurved and held upwards, often overtopping the front part of the body (exceptions are in the subtribe Timeparthenina, in which the swelling is concentrated towards the front of the abdomen and hence it cannot be recurved). They also have relatively long legs for staphylinids, though this may be correlated with supporting their enlarged abdomens. Corotocins appear to make their living by imitating the nymphs of the termites they live amongst, and being fed and looked after by the adult termites.

*The development of the physogastric abdomen is something that may be worthy of attention. Stenogastric individuals (without swollen abdomens) have been identified for some corotocin species; for Thyreoxenus major, a series of specimens was identified by Seevers (1957) that he felt indicated that adults initially emerged as stenogastric, then developed physogastry over time. However, physogastric and stenogastric individuals differ not only in the size of the abdomen, but also in the shape and proportions of leg segments. This could be a problem, because insect growth generally doesn't work that way.

Line drawing of Timeparthenus, showing the non-reflexed abdomen. Note also how the elytra have been pushed forward above the pronotum. From Seevers (1957).

How they achieve this trick has been subject to some discussion, but is still not really resolved. Inquilines, by their very nature, tend to be uncommon and difficult to find, so many aspects of their biology remain mysterious. Many authors have assumed that the physogastric abdomen is associated with the production of chemical exudates or other substances that mimic those produced by the termite nymphs, and termitophilous staphylinids in other lineages have been shown to produce the same cuticular hydrocarbons as their termite hosts (Howard et al. 1982). However, it has been suggested that members of one particular corotocin subtribe, the Corotocina, may take the mimicry a step further. In some species of this subtribe, the abdomen is not only swollen but possesses odd sausage-like appendages:

Lateral view of Coatonachthodes ovambolandicus, from Kistner (1968).

In one species possessing such appendages, Spirachtha mirabilis, its host termites have been observed licking them, suggesting that they may be a focus for exudate production. However, Kistner (1968) suggested that they may serve a further function, the possibility of which becomes most clear when they are seen from above:

Dorsal view of Coatonachthodes ovambolandicus, from Kirstner (1968).

The appendages, together with strategically placed abdominal constrictions, may turn the beetle's abdomen into a tactile facsimile of one of the termites themselves! So close was the mimicry, Kistner felt, that he used differences between the abdomens of Coatonachthodes ovambolandicus and another corotocin, Spirachthodes madecassus, to predict morphological differences between their respective hosts. Kistner's predictions were later tested by Sands & Lamb (1975), who showed that Kistner had been both wrong and right. Workers of the host species of S. madecassus, Kaudernitermes kaudernianus, did not possess the features predicted by Kistner. However, the second-instar nymphs did! Sands and Lamb refined the mimicry hypothesis to suggest that it was the nymphs, not the workers, that the beetles were imitating. An interesting corollary of this refinement is that very young termite nymphs apparently do not yet exhibit the chemical characteristics of their home colony, so a first- or second-instar-imitating beetle would not necessarily have to mimic the host chemistry itself.

Termitophya emersoni, a less morphogically specialised corotocin, from Seevers (1957).

For those Corotocini without the abdominal appendages of the Corotocina, of course, the chemical mimicry hypothesis perhaps remains the most likely. It is worth noting, too, that tactile and chemical mimicry are not mutually exclusive. Tactile mimicry is also not exclusive of a third suggested function for the abdominal appendages, that they may function as decoys if one of the host termites was to attack the beetle, in the same way that some lizards drop their tails. Whatever the explanation, there can be no doubt that these are truly remarkable beasts.

REFERENCES

Howard, R. W., C. A. McDaniel & G. J. Blomquist. 1982. Chemical mimicry as an integrating mechanism for three termitophiles associated with Reticulitermes virginicus (Banks). Psyche 89: 157-168.

Kistner, D. H. 1968. Revision of the African species of the termitophilous tribe Corotocini (Coleoptera: Staphylinidae). I. A new genus and species from Ovamboland and its zoogeographic significance. Journal of the New York Entomological Society 76 (3): 213-221.

Sands, W. A., & R. W. Lamb. 1975. The systematic position of Kaudernitermes gen.n. (Isoptera: Termitidae, Nasutitermitinae) and its relevance to host relationships of termitophilous staphylinid beetles. J. Ent. (B) 44 (2): 189-200.

Seevers, C. H. 1957. A monograph on the termitophilous Staphylinidae (Coleoptera). Fieldiana: Zoology 40: 1-334.

Life with Termites

Termitusodes lativentris. Image from Seevers (1957).

The Staphylinidae are one of the largest (over 46,000 species) and most easily recognisable of the commonly accepted beetle 'families'. Among other things, they can be readily distinguished from other beetles by the reduction of the elytra so that they no longer cover the abdomen, similar to what is seen in the earwigs. The most familiar staphylinids are relatively large predatory species (known as rove beetles or devil's coach-horses) but the family includes a wide variety of other forms.

The animal rather poorly illustrated at the top of the post is a member of the subtribe Termitusina in the subfamily Aleocharinae. Termitusina are found in tropical Africa where they live within the colonies of certain species of termite. The image doesn't show the distinguishing features of this group very well, unfortunately, but if you look carefully (and perhaps use a bit of imagination) you may be able to make out the strongly deflexed head and ninth abdominal tergite divided between two elongate halves. Unlike many termite-associated staphylinids, Termitusina of the genera Termitusa and Thoracotusa do not generally exhibit physogastry (a swollen abdomen). Termitusodes, the third genus in the subtribe, differs from the other two genera in this respect, though it still comes nowhere near the level of physogastry found in some termite-associated staphylinids.

I haven't been able to find out whether the Termitusina are in some way social parasites of their host termites or whether they are finding their food in the nest some other way (such as by scavenging or feeding on fungi) but the association is undoubtedly a close one. Termitusina are, as a rule, host specific (Jacobson & Kistner, 1975). Termitusa are found only in nests of the termite genera Cubitermes and Noditermes, Thoracotusa is found with Thoracotermes, and Termitusodes has been found with Cubitermes and Pericapritermes magnificus. Pericapritermes often nest in association with Cubitermes (they may occupy abandoned Cubitermes nests or they may invade the nest while the Cubitermes are still living there) and it seems likely that this association is what allowed Termitusodes to change hosts at some point in its history.

REFERENCES

Jacobson, H. R., & D. H. Kistner. 1975. Numeric analyses of relationships of genera and species of the subtribe Termitusina (Coleoptera: Staphylinidae). Systematic Zoology 24 (2): 191-198.

Seevers, C. H. 1957. A monograph on the termitophilous Staphylinidae (Coleoptera). Fieldiana: Zoology 40: 1-334.