Rove by the Riverside

The Staphylinidae, commonly known as the rove beetles, are one of the most diverse of the recognised beetle families. Indeed, thanks to their habit in recent years of glomming up lineages previously treated as distinct families like the pselaphids and scydmaenids, they now rival the weevils of the Curculionidae for the position of largest of all recognised animal families. But for their diversity and ubiquity, staphylinids are comparatively poorly studied, owing to a not-unwarranted reputation for taxonomic recalcitrance (the relatively soft bodies of many staphylinids mean they often do not handle well with standard methods for examining beetles). Perhaps the most neglected of all staphylinid subgroups is the subfamily Aleocharinae. Aleocharines are often minute (the average aleocharine is only a couple of millimetres in length) and their identification often requires resolving features that lie at the very limit of what can be seen with a standard dissecting microscope. Nevertheless, aleocharines are remarkably diverse and among their representatives are the representatives of the genus Parocyusa.

Parocyusa americana, from Brunke et al. (2012); scale bar = 1 mm.

Typical aleocharines have what is thought of as the 'standard' body form for staphylinids, with short, square elytra that do not cover the long, flexible abdomen (though I should mention that, with the aforementioned assimilation of the pselaphids and scydmaenids, I suspect there may now be more 'non-standard' staphylinid species than 'standard' ones). For the most part, they can be distinguished from other staphylinid subfamilies by the position of the antennae, with their insertions placed behind the level of the front of the eyes. Aleocharines are divided between numerous tribes; Parocyusa is included in the tribe Oxypodini, a heterogenous group of relatively unspecialised aleocharines. Notable features distinguishing Parocyusa from other aleocharine genera include legs with five segments to each tarsus, a frontal suture between the antennal insertions, the median segments of the antennae being longer than wide, the head not having a well defined 'neck', the sides of the pronotum not being strongly deflexed downwards (so the hypomeron, the lateral section of the pronotum, is clearly visible in side view), and deep transverse impressions across the third to fifth abdominal tergite but not across the sixth tergite or across the sternites (Newton et al. 2001). Members of the genus are a bit over three millimetres in length.

Species of Parocyusa are found widely in the Holarctic realm; I've found reference to species from Europe, Korea, and northeastern North America (I should also note that I've also encountered dark allusions to recent rearrangements of the generic status of some of these species but without access to such revisions I'm going to stick with what I can find). I haven't found any reference to their specific diet but I suspect that they would be micropredators, a common lifestyle for staphylinids of their kind. Parocyusa species are associated with running water, living among the gravel and sand alongside stream beds (e.g. Brunke et al. 2012). As such, these and other aleocharines have received attention in ecological studies: the higher the diversity of staphylinids present, the more healthy the ecosystem is likely to be.

REFERENCES

Brunke, A. J., J. Klimaszewski, J.-A. Dorval, C. Bourdon, S. M. Paiero & S. A. Marshall. 2012. New species and distributional records of Aleocharinae (Coleoptera, Staphylinidae) from Ontario, Canada, with a checklist of recorded species. ZooKeys 186: 119–206.

Newton, A. F., M. K. Thayer, J. S. Ashe & D. S. Chandler. 2001. Staphylinidae Latreille, 1802. In: Arnett, R. H., Jr & M. C. Thomas (eds) American Beetles vol. 1. Archostemata, Myxophaga, Adephaga, Polyphaga: Staphyliniformia pp. 272–418. CRC Press: Boca Raton.

Raffrayia

In previous posts, I have introduced you to various representatives of the Pselaphinae, bizarre-looking little gorgon-headed beetles dwelling in soil. But as with all elements of the world's biodiversity, I have not even begun to scratch the surface of what this group has to offer. So for today, a post on another pselaphine genus: the African Raffrayia.

Male Raffrayia dilatata, from Jeannel (1955).

The genus Raffrayia was first established by Reitter in 1881 for a species found in Ethiopia and since then over twenty species have been recognised. The great majority of these have been from southern Africa, in particular from various locations in the Cape Province. Only the meerest handful have been described from scattered localities in east Africa. Nevertheless, it would not be at all surprising if this disparity between regions turns out to be in part an artefact of study effort; there may be more species yet to be described.

The most distinctive feature of the genus is one or two rings each of small button-like nodules on the median segments of the antenna (I am unable to guess the functional significance of these, if any). Jeannel (1955) recognised a number of smaller genera closely related to Raffrayia that share these antennal nodules but differ in having a more elongate basal segment on the abdomen and/or being uniformly flightless forms with the humeri ('shoulders') of the elytra reduced (flightless Raffrayia [see below] retain more distinctly pronounced humeri). Both of these features are derived and these segregate genera may well be expected to be derivatives of Raffrayia. Jeannel also distinguished two subgenera Raffrayia sensu stricto and Raffrayola based on the structure of the first abdominal segment. Raffrayola is restricted to southern Africa whereas Raffrayia sensu stricto is found across the genus' range.

Sexual dimorphism within the genus is strong: males are winged but females are flightless. Elytra are somewhat reduced in females as a result (but again, not as much as in consistently flightless genera). Unfortunately, while we can make some obvious inferences from this about their relative life styles, there seems to be little in the way of direct observations on how Raffrayia spend their lives.

REFERENCE

Jeannel, R. 1955. Les psélaphides de l'Afrique australe. Mémoires du Muséum National d'Histoire Naturelle, nouvelle série, Série A, Zoologie 9: 1–196.

Rove, If You Want To

Rove beetle Staphylinus erythropterus, copyright James K. Lindsey.

The Staphylinidae, rove beetles and related forms, is an absolutely massive array of insects. In fact, thanks to some relatively recent waves of the redefinition wand, the Staphylinidae is not only the largest recognised family of beetles but the largest family of animals of any kind. It even beats out the Curculionidae weevils that were the previous fore-runners. One might think that such a diverse group of animals would be the subject of extensive attention but that is simply not the case. I've commented before that part of the reason for this neglect is that staphylinids are a simply horrid group to work with but they still deserve a better look.

Devil's coach-horse Ocypus olens in a threat display, from Wildlife Insight. The white blebs visible at the end of the abdomen represent glands producing an unpleasant odour.

The original rove beetles belong to the tribe Staphylinini, a cosmopolitan group with more than 5300 known species and probably many more yet to be described. They are mostly active predators of other arthropods, hence the name 'rove beetle' in reference to their roving habits. One particularly large species (up to about three centimetres in length), Ocypus olens, has garnered the moniker of 'devil's coach-horse'. Several genera are found in association in ants and a termitophilous genus Sedolinus was recently described from South America (Solodovnikov 2006). The exact nature of its association with its termite hosts remains uncertain though it is worth noting that it shows less marked morphological adaptations than other termitophilous staphylinids. The South American Amblyopinus and closely related genera in South America and Australia are found amongst the fur of rodents and small marsupials. Because they are often attached to their host by the mandibles, they were long believed to be parasites feeding on blood or skin secretions. However, further studies found that they do not bite into the host but instead grip to its fur. And rather than feeding on the host itself, they feed on other, actually parasitic arthropods also present on the host (Ashe & Timm 1987).

Edrabius peruvianus, a member of the Amblyopinus group of mammal associates, copyright Stylianos Chatzimanolis.

The classification of Staphylinini is currently in the progress of going through a major shake-up. Not only were many of the taxa within the tribe previously poorly defined, what definition they had was mostly taken from Holarctic taxa. Species found in other parts of the world had largely been classified by finding what Holarctic taxon they most resembled, at least superficially, slotting them therein and then jumping on them until they could be made to fit. A prime example of this awkwardness revolves around the genus Quedius, to which species have been assigned from around the world. Molecular phylogenetic studies have found that a cosmopolitan Quedius represents a polyphyletic grouping (Brunke et al. 2016). Southern Hemisphere taxa assigned to Quedius or believed closely related are not only not immediate relatives of the true European Quedius, but they have been assigned to entirely distinct subtribes representing strongly divergent lineages in the Staphylinini.

REFERENCES

Ashe, J. S., & R. M. Timm. 1987. Predation by and activity patterns of 'parasitic' beetles of the genus Amblyopinus (Coleoptera: Staphylinidae). Journal of Zoology 212: 429–437.

Brunke, A. J., S. Chatzimanolis, H. Schillhammer & A. Solodovnikov. 2016. Early evolution of the hyperdiverse rove beetle tribe Staphylinini (Coleoptera: Staphylinidae: Staphylininae) and a revision of its higher classification. Cladistics 32 (4): 427–451.

Solodovnikov, A. 2006. Adult and larval descriptions of a new termitophilous genus of the tribe Staphylinini with two species from South America (Coleoptera: Staphylinidae). Proceedings of the Russian Entomological Society, St. Petersburg 77: 274–283.

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.