Restoring the dignity of staphylinids everywhere
Longtime readers of the original, largely-defunct American Beetles may recollect a series of posts back in the day, focusing on strange and horrifying things that beetles do. One of the best examples, of course, is the demure and lovely (also wingless and eyeless) leiodid Platypsyllus castoris, a beetle so weird it was once placed in its own order (and for a long time, its own family).
Platypsyllus, also known as the “beaver beetle,” is an obligate ectoparasite of (yes) beavers. It is also the only beetle demonstrated (by Wood, 1965) to be a genuine parasite of mammals; species in a number of other beetle families are phoretic on mammals, meaning that they cruise around enjoying a free ride, be it for purposes of protection, dispersal, or (in the case of the delightful South American staphylinid Amblyopinus) feeding on various smaller arthropod parasites of the vertebrate host.
Ashe and Timm (1987) noted that Amblyopinus seems to enjoy a mutualistic relationship with its host, the Mexican volcano mouse: when placed on a non-host rodent species, the beetles were immediately scratched off and frequently eaten. Other noted mammal-phoretic beetles include several rodent- (or desman-) associated leiodid genera, the amblyopinine staphylinids Myotyphlus and Edrabius, and the erotylid Loberopsyllus, which to my understanding is found only on hamsters.
What you should know is: I was looking up some references on inquiline and phoretic habits in staphylinoids the other day, and came across what might be the greatest staphylinoid paper ever written.
This indignant article takes to task the idea that the hapless staphylinid Myotyphlus is a true parasite of rats. This is thanks to “personal communications” from a vigilant rodent researcher, who (after conducting deeply personal investigations of “2,000 Rattus assimilis“) reveals the following:
Obviously, this captures the imagination. Being phoretic on mammals may be old hat for staphylinids, but: anus specialists? That’s news to me. You’ve probably heard of the South American scarabs who specialise on sloth dung; in order to colonise the dung whilst it’s still fresh and malleable, they ride around on the sloth, perpetually vigilant for the next deuce to drop. I have also heard rumours of Australian Onthophagus, another scarab, being discovered in shocking abundance on the nether regions of kangaroos. This kind of behaviour may be acceptable for scarabs, but I was surprised to hear about staphs stooping to this particular level.
Anyhow, Hamilton-Smith and Adams would like you to know that Myotyphlus has since been found living wild and free in subterranean mounds of bat guano, and is therefore IN NO WAY an obligate ectoparasite, nor indeed a parasite at all. I think I speak for all staphylinoid enthusiasts when I say I shall breathe slightly easier knowing that Myotyphlus is no obligate associate but merely a facultative inhabitant of the rat anus microhabitat.
Ashe, J. S., and Timm, R. M. 1987. Probable mutualistic association between staphylinid beetles (Amblyopinus) and their rodent hosts. Journal of Tropical Ecology 3:177-181.
Wood, D. M. 1965. Studies on the beetles Leptinillus validus (Horn) and Platypsyllus castoris Ritsema (Coleoptera: Leptinidae) from beaver. Proceedings of the Entomological Society of Ontario 95: 33-63.