Ant wars: combat strategies, territory and nest defence in the leaf-cutting ant Atta laevigata

Abstract

Two laws have been highlighted when discussing combat strategies in ants: the linear law (in a series of one-to-one conflicts, a few good fighters are better than many poor fighters) and the square law (if all individuals are vulnerable to attack, numerous fighters are more advantageous than a few good fighters). The leaf-cutting ant, Atta laevigata, responded to a simulated vertebrate threat by recruiting many soldiers (large workers), but responded to conspecific and interspecific ant threats by recruiting mainly small ants. In staged intraspecific interactions in the field between adjacent nests, ants were reluctant to fight on unmarked land and often retreated onto established marked trails, retreated to the nest entrance which they then capped or guarded, or immediately began marking the battle site with Dufour's gland secretion. These results indicate that the territorial behaviour of A. laevigata is part of a complex system to defend resources, where the defence of one resource (food) can develop into the defence of another (the nest). During the build-up of a war, once individuals from two nests met, recruitment changed from medium and large ants to mainly small ants. It is suggested that A. laevigata uses the soldier caste to defend the nest against large organisms and recruits numerous small ants in response to conspecific and interspecific ant threats following the square law.