We observed Tetramorium caespitum (Hymenoptera: Formicidae) in large swarms outside nest entrances. Upon observation it was evident that individual ants were locked together in pairs with their mandibles in a large battle. No explanation for fighting was apparent.

We explored several hypotheses: (1) That the fighting was the result of a slave raid, (2) territoriality, and (3) a colony breakdown. To distinguish the possibilities, samples were taken from 10 battles. Twenty fighting pairs were separated, labeled, and point mounted for identification. Pairs were identified and both individuals were consistently T. caespitum.

Virulent territoriality occurs most frequently between species that are closely related who compete for similar resources. T. caespitum however, is described as seldom aggressive in alien conspecific encounters. Territoriality was rejected because the conflict seemed concentrated over a single nest.

We then excavated colonies of T. caespitum and made lab observations to explore colony conflict resulting in a breakdown of the colony. Our lab studies suggest that this polygynous species is unstable.