Wood ants, i.e. species of the subgenus Formica s. str., are known to be temporary social parasites of ants of the subgenus Serviformica For. However, not only Serviformica colonies are used by young wood ant queens to start their own colonies. They are also able to take over colonies, at least queenless ones, of related species of the subgenus Formica s. str. This study followed five experimental colonies of wood ants - three of hybrid Formica aquilonia x F. polyctena, one of F. aquilonia-like form, and one of F. polyctena - artificially planted on islands of the Tvńrminne archipelago, S Finland. After some years, the species identity of all colonies was F. polyctena, i.e. four of them had been taken over by heterospecific queens, whose offspring gradually replaced the old workers. These findings, together with already documented existence of hybrids in wood ants, partly explain the interspecific and intracolonial, until recently unaccountable, variability in wood ants of the Formica rufa group, frequently observed in southern Finland.
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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.
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