Perhaps the best-known case of xenobiosis is that of the shampoo ant,
originally described by Wheeler (1903, 1910), in whichFormicoxenus
provancheri(=Leptothorax emersoni) parasitizes colonies ofMyrmica
incompleta (= Myrmica brevinoda). Ants in the tribe Formicoxeni
(=Leptothoracini) tend to be small and inconspicuous and often nest in
tiny cavities in the soil or in hollow twigs, stems and nuts. They are
common elements in the north temperate ant fauna, and nest densities can
be very high in local areas. Interestingly, they also appear to be especially
prone to the formation of socially parasitic relationships (Alloway, 1980,
1997; Allowayet al., 1982; Stuart and Alloway, 1982, 1983; Buschinger,
1986; Hölldobler and Wilson, 1990).M. incompletaforms nests in soil,
often in clumps of moss or under logs or stones, especially in damp areas;
andF. provancherinests in the soil, next toM. incompletanests, joined to
them by short galleries. TheFormicoxenusmove freely through the nests
of their hosts but their galleries are too small to permit entrance by the
Myrmica. TheFormicoxenusappear to rely almost exclusively on liquid
food obtained from their hosts. TheFormicoxenusworkers solicit regurgi-
tation from theMyrmicaworkers and occasionally mount them and ‘lick’
them in an excited manner, moving their softer mouth-parts back and
forth over the host ant’s body, the shampoo behaviour of Wheeler’s origi-
nal description. OtherFormicoxenusspecies have similar associations
with variousMyrmica,FormicaandManicaspecies (Francoeuret al.,
1985).
Wheeler (1925) reported an additional case of xenobiosis, in which
the small myrmicine antMegalomyrmex symmetochusparasitizes the
fungus-growing ant,Sericomyrmex amabilis. The parasite and the host
both maintain their broods within the fungus gardens of the host, but
apparently tend them quite separately; and the parasite feeds on the
fungus and occasionally licks the bodies of its host.Mixed colonies
Mixed colonies typically represent some form of facultative or obligatory
social parasitism and three major forms are recognized: temporary social
parasitism, slavery (or dulosis) and inquilinism. These forms share certain
common elements and might have evolved from one to another in certain
phylogenetic lines.Temporary social parasitism
In temporary social parasitism, a newly mated queen of the parasite
species manages to secure adoption into a colony of the host species
by some mechanism, often involving aggression, stealth, some form of
apparent ‘conciliation’ or a combination of these tactics. Subsequently,
usurpation of the host colony is completed, as the host queen or queens
are killed either by the parasite or by her own workers. The parasite queen
then assumes the egg-laying chores of the colony, with the host workers320 R.J. Stuart