Corpse carrying in ants (Hymenoptera: Formicidae) : behavioural side effect of aggressive arousual or competitive signaling?

Some literature reports show that ants use bodies of their dead nestmates and other insect remains in conflict situations. The paper describes such phenomenon in a Formica rufa L. colony brought into conflict with a F. cinerea Mayr colony when the former tried to extend its own territory at the expense of the latter. A territorially stable F. rufa colony, neighbouring the same F. cinerea colony, served as control. Workers of the expansive F. rufa colony were repeatedly observed to carry numerous ant corpses, empty pupal cocoons and insect leftovers from their nest to the place of confrontation with F. cinerea, on a much bigger scale than workers of the stable F. rufa colony. Corpse-carrying intensity was not correlated with the general activity level of foragers which suggests that corpse carriers could be a separate task group. Workers of a small colony of F. cinerea were also observed to surround their nest entrance with corpses of their nestmates and prey remains, taken out from inside the nest, in response to intensified traffic of workers of F. rufa in the vicinity of their nest. These results are discussed in the context of a possible interrelation between ant aggressive behaviour and transport behaviour. Two hypotheses are proposed to explain the observed phenomenon: (1) explaining it as a by-product of the aggressive arousal of workers, and (2) ascribing to it a possible signalling function in conflict situations.