The Descent of Man

males of one of the saw-flies (Tenthredinae)
"have been found fighting together, with their
mandibles locked." As M. Fabre speaks of the
males of Cerceris striving to obtain a particular
female, it may be well to bear in mind that insects
belonging to this Order have the power of
recognising each other after long intervals of
time, and are deeply attached. For instance,
Pierre Huber, whose accuracy no one doubts,
separated some ants, and when, after an interval
of four months, they met others which had
formerly belonged to the same community,
they recognised and caressed one another with
their antennae. Had they been strangers they
would have fought together. Again, when two
communities engage in a battle, the ants on the
same side sometimes attack each other in the
general confusion, but they soon perceive their
mistake, and the one ant soothes the other. (58.
P. Huber, 'Recherches sur les Moeurs des
Fourmis,' 1810, pp. 150, 165.)