Facultative and obligate slave making in Formica ants

Here we show for the first time that the presumed facultative slave-making ant Formica subintegra does not activate outside its nest until July and Au gust, when it raids slaves. A comparative behavioral study of seasonal and daily activities, retrieval of prey, and nest maintenance of F. subintegra, the obligate slavemaker Polyergus breviceps, and the facultative Formica s ubnuda, shows that the behavioral repertory of F. subintegra closely resemb les that of P. breviceps and clearly differs from the repertory of F. subnu da. Unlike P. breviceps, F. subintegra has retained some nest-building acti vity which, owing to lack of competence, does not contribute to nest mainte nance. We suggested earlier that F. subintegra is probably an obligate slav emaker, because it always has in its colonies a large proportion of slaves of the total workforce, whereas F. subnuda fares well even without slaves, This, coupled with no foraging in early summer and a raiding period later o n, strongly suggests that F. subintegra is an obligate slave-making ant.