EXPLOITATION OF AN ANT CHEMICAL ALARM SIGNAL BY THE ZODARIID SPIDER HABRONESTES BRADLEYI WALCKENAER

Intraspecific signals are vulnerable to exploitation by predators that are not the targets of the signal. This cost has been documented for several acoustic, visual and chemical signals, but not for chemical al arm pheromones. We reveal a novel form of exploitation of an ant alarm pheromone by the cursorial spider Habronestes bradleyi (Zodariidae), a specialist predator of the highly territorial and aggressive meat an t Iridomyrmex purpureus. We demonstrate experimentally that H. bradley i locates I. purpureus workers engaged in territorial interactions wit h conspecifics, by using the alarm pheromone of the ants as a cue. The spiders are attracted to an airborne cue, identified as the alarm phe romone 6-methyl-5-hepten-2-one, which is produced by injured or alarme d I. purpureus workers but not by inactive I. purpureus, or injured wo rkers of other sympatric ant species. These data demonstrate a novel c ost of producing alarm pheromones.