The results of an investigation on the division of labour in the guest
-ant Fomicoxenus provancheri, conducted by observing colonies containi
ng individually marked adults, are presented. Five colonies of Formico
xenus were installed in the laboratory with their hosts, Myrmica incom
pleta, in order to document, over 10 d, the location of individuals as
well as individual and interactive types of behaviour. The results sh
ow that each colony of Formicoxenus consists of three groups: a group
of nurses who remain in the Formcoxenus nest (some 21% of the colony's
members); a group of scouts who spend most of their time in the exter
nal area (18%) and a very large group of individuals specialized in li
cking ('shampooing') the host to obtain regurgitations (61%), who esse
ntially remain in the Myrmica nest. Division of labour in Formicoxenus
appears to be a special adaptation to the xenobiotic way of life. The
apparent link between social structure and the probability of profiti
ng from trophallactic exchanges with the host species could lead to in
teresting predictions on the division of labour in other guest-ants.