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.

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.