This "very interesting, though repulsive, insect" (to use the words of Hebard in 1927) is a member of today's Taxon of the Week, the Neodermaptera. Neodermaptera is the clade containing all living members of the Dermaptera, the earwigs, distinguished from various stem groups of the Dermaptera by features such as three-segmented tarsi and the lack of veins in the forewings (Engel 2003). Earwigs are one of the few groups of insects other than beetles to have the forewings hardened into elytriform cases, which in earwigs have also been greatly reduced in size (in earwigs, the hardened forewings are referred to as 'tegmina' rather than 'elytra', but these seem to be just different words for much the same sort of thing). The rarely-seen hindwings remain folded under the tegmina unless the earwig is flying (which they do not often do) and are simply bizarre. One of the characteristics of polyneopterans, the group of insects including crickets, cockroaches, earwigs and various others, is a tendency towards enlargement of the anal fan, the posterior part of the wing; in earwigs, the anal fan of the hindwing has become enlarged to the point that the wing is almost entirely anal fan with the anterior parts of the wing greatly reduced and crammed into a small toughened section towards the base. One of the stories floating about to supposedly explain the origin of the name 'earwig' claims that it is a corruption of 'ear-wing'. While the wings are indeed ear-shaped, the story rather loses credibility in face of the detail that the average person would probably never see them.
The other distinctive feature of most living earwigs is the development of the cerci at the end of the abdomen into a pair of large, hard forceps. The forceps are used for defense as well as capturing prey in those species that eat animal matter (most earwigs are omnivorous); they may also be used to help fold the wings under the tegmina. In most species, the males have heavier forceps than the females. The only earwigs to have filamentous cerci rather than forceps are the Arixeniidae and Hemimeridae, two families that live in association with mammalian hosts. Arixeniids (such as Arixenia in the top picture) are about 2 cm long and live on bats in south-east Asia; hemimerids are about half that size and live on African giant rats. Not are they distinctive among earwigs, they are the only known quasi-parasitic polyneopterans—I say 'quasi'-parasitic because they probably feed more on dead skin and host secretions than the actual living host itself. The arixeniids probably feed mostly on the rich deposits of bat poo in host roosting sites. Because of the lack of forceps and other features, these two families have often been placed in separate suborders from the remaining earwigs; at least one author argued that hemimerids should be removed from Dermaptera entirely and treated as a separate order. However, the current consensus is that the two families are probably derived from more normal earwigs, with their distinctive features being adaptations to their symbiotic lifestyles.
Another distinctive feature of the two mammal-associated families is that they are live-bearers. In all other families, the female lays a batch of eggs, usually in a burrow, that she watches over until the young hatch out. She continues to protect her young for their first one or two instars; after that they must fend for themselves. In fact, if the young do not move out quickly enough, their mother will eat them (Rentz & Kevan, 1991). Something, perhaps, to be kept in mind by all those parents who feel their adult offspring are taking too long to get their own place.
REFERENCES
Engel, M. S. 2003. The earwigs of Kansas, with a key to genera north of Mexico (Insecta: Dermaptera). Transactions of the Kansas Academy of Science 106 (3-4): 115-123.
Hebard, M. 1927. Studies in Sumatran Dermaptera. Proceedings of the Academy of Natural Sciences of Philadelphia 79: 23-48.
Rentz, D. C. F., & D. K. McE. Kevan. 1991. Dermaptera (earwigs). In: CSIRO. The Insects of Australia, 2nd ed., vol. 1, pp. 360-368. Melbourne University Press.
Interesting to note in regards to the name, is that although the name itself "earwig" isn't corresponding to the Swedish term "tvestjärt" (double-tail), the earwigs are notorious in the popular consciousness for having the bad habit of crawling into the ears of sleeping people. Whilst this most likely is an old urban legend (I remember my grandfather went on and on about it, as did most of his generation) I think that if similar superstition exists in the English consciousness, the peculiar name of earwig has found a likely explanation.
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