INTENSIVE FOOD SEARCHING IN HUMID PATCHES: ADAPTATION OF A MYRMICINE ANT TO ENVIRONMENTAL CONSTRAINTS

We tested if foragers of the ant Decamorium decem control the sinuosity of their food searching paths and their speed in order to concentrate their activity in areas of high prey density, humid patches of leaf-litter, during the dry season. In experimental situation I simulating the wet season (uniformly humid arenas) food searching paths were erratic and homing paths direct. In situation II simulating the dry season (dry arenas with a humidified disk) the sinuosity of the searching paths increased and the speed decreased when workers moved from the dry arenas to the humidified disks; homing paths were again direct. Thanks to comparisons with situation I, we argue that in situation II workers first oriented themselves toward the humidified disks (sinuosity significantly lower on the dry than on the wet arenas; non-significant difference for speed). Otherwise, we show that the intensive search on the humidified disks depends only on a decrease in speed (significantly lower on the humidified disks than on the wet arenas of situation I; nonsignificant difference for sinuosity), with workers switching from active searching to ambush when prey are absent.