Xenodusa reflexa (Walker)

Xenodusa reflexa - dorsal habitus.

Introduction & Bionomics

Rove Beetles (Staphylinidae) of the tribe Lomechusini (Aleocharinae) have a fascinating ecology. Wasmann (1897) studied this group in Europe and wrote (translated from the German by Wheeler, 1907):

The Lomenusa group, embracing the Palearctic genera Lomenusa and Atemeles and the Nearctic genus Xenodusa, contains, from an ethological point of view, the most interesting and at the same time the largest of the true ant guests (symphiles) of the Holarctic region. These staphylinids, which belong to the subfamily Aleocharine, are treated by the ants like their own kith and kin, live in antennary communication with them, are cleaned and licked and occasionally also carried about; they are fed from the mouths of the hosts, although they are able to eat independently and frequently devour the ant brood.
"The ants are especially attracted to these beetles on account of the prominent tufts of yellow hairs on the sides of their abdomens which are licked by the host with evident satisfaction. Not only do these beetles themselves live as guests among the ants, but the same is also true of their larvae.

Xenodusa reflexa - appeasement glands.

"The larvae of Lomenusa and Atemeles are reared by the ants like their own brood; they are licked, fed with regurgitated food, and before pupation, covered or embedded in cells like their own larvae. When the nest is disturbed they are carried by the ants to a place of safety in preference to their own larvae and pupae. The predilection of the ants for these adopted larvae is all the more remarkable because they are the worst enemies of the ant brood and consume enormous numbers of eggs and larvae of their hosts. This brood parasitism, in fact, causes the development of abortive individuals intermediate between female and worker castes, and these intermediates, which In have called pseudogynes, gradually bring about a degeneration of the parasitized colonies."

Experiments by Hölldobler (1971) have shown that adult beetles are adopted by an ant colony by means of a ritual involving chemical communication. Beetles encountering an ant tap it with their antennae and elevate the tip of their abdomen. The ants then lick secretions emitted from "appeasement glands" on its tip. These substances apparently suppress aggressive behaviour towards intruders. The ant then proceeds to lick secretions from a series of "adoption glands" along the lateral margins of the abdomen and only then will the beetle be admitted into the ant colony.

Xenodusa reflexa - lateral habitus.

Xenodusa reflexa (Walker) in Canada

In North America Hoebeke (1976) published the authoritative account and revision of the genus. There are five species, two of which, Xenodusa reflexa (Walker) and Xenodusa cava (LeConte), have been hitherto recorded from Canada, the former from British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, and Quebec; the latter only from Ontario.

Pictured here is an individual collected Harold T. Stultz on June 6, 1941 in Berwick, Kings County, Nova Scotia, Canada - the first record of this genus in Atlantic Canada. Further research needs to be done to determine the extent of this species distribution here. It is possible that an isolated colony of X. reflexa exists in the Annapolis Valley.

References

Hoebeke, E. R. 1976. A revision of the genus Xenodusa (Staphylinidae: Aleocharinae) for North America. Sociobiology 2(2): 109-143.

Hölldobler, B. 1971. Communication between ants and their guests. Scientific American 224(3): 86-93

Wasmann, E. 1897. Zue Biologie und Morphologie der Lomenusa Gruppe. Zool. Anzeig. 20: 463-471.

Wheeler, W. M. 1907. The polymorphism of ants, with an account of some singular abnormalities due to parasitism. Bulletin of the American Museum of Natural History 23: 1-93.

Many thanks to Richard Hoebeke of Cornell University for assistance in determination.