ORIENTATION AND FORAGING MOVEMENTS IN A PATCHY ENVIRONMENT BY THE ANTSERRASTRUMA-LUJAE (FORMICIDAE-MYRMICINAE)

Serrastruma lujae ants individually search for collembolans in the lea f litter of humid tropical forests. During the dry season, collembolan s aggregate in wet patches randomly scattered in the dry litter where numerous single workers come hunting from their nest. We simulated thi s situation in the laboratory, and observed that workers seem to be ab le to use the humidity gradient direction to efficiently orient themse lves towards a wet patch. Once the patch has been reached, they exhibi t area-concentrated searching, consisting, in particular, of adopting a high sinuosity and a low speed. After capturing a collembolan, the a nts return to their nest along nearly straight paths. This ability may rely on a spatial memory of the nest location by means of a path-inte gration process. In the absence of prey, however; various behaviours w ere observed after an unsuccessful search. Comparisons between these d ata and the results obtained with a homogeneously wet environment simu lating the rainy season situation showed that these ants do not simply respond to the humidity level but are also sensitive to the degree of patchiness of their environment. They can therefore be said to be abl e to adapt suitably to the considerable climatic changes they encounte r during the year.