Field studies of cleptobiotic behavior in the neotropical ant Ectatomma ruidum (Hymenoptera, Ponerinae).

In the ponerine ant Ectatomma ruidum, under high nest density conditions, hunting areas of neighboring colonies partly overlap and some workers can enter a foreign nest to rob food reserves (cleptobiosis). In order to enhance foraging competition between E. ruidum colonies, a large quantity of small prey was provided as a single fixed food source during 3 replications, in a Mexican coffee plantation. The food source exploitation was done by "facultative" or "exclusive" cleptobiosis, according to the existence or absence of any direct provisioning to this source. Exclusive cleptobiotic nests were, on average, more distant from the source (near to 60% more) than colonies foraging directly on it. The activity of previously marked thief ants was studied during 4 weeks, focusing on the individual fidelity to the same target nest, the duration of intrusions with or without food robbing and the rejections of intruders by resident workers. We discuss the ecological impact of cleptobiosis as an effective foraging strategy and the camouflage hypothesis proposed as an evasive mechanism of the nestmate recognition system.