Interpopulation variation in the risk-related decisions of Portia labiata, an araneophagic jumping spider (Araneae, Salticidae), during predatory sequences with spitting spiders.

The extent to which decision-making processes are constrained in animals with small brains is poorly understood. Arthropods have brains much smaller and simpler than those of birds and mammals. This raises questions concerning limitations on how intricate the decision-making processes might be in arthropods. At Los Baños in the Philippines, Scytodes pallidus is a spitting spider that specialises in preying on jumping spiders, and Portia labiata is a jumping spider that preys on S. pallidus. Scytodid spit comes from the mouth, and egg-carrying females are less dangerous than eggless scytodids because the female uses her chelicerae to hold her eggs. Held eggs block her mouth, and she has to release them before she can spit. The Los Baños P. labiata sometimes adjusts its tactics depending on whether the scytodid encountered is carrying eggs or not. When pursuing eggless scytodids, the Los Baños P. labiata usually takes detour routes that enable it to close in from behind (away from the scytodid's line of fire). However, when pursuing egg-carrying scytodids, the Los Baños P. labiata sometimes takes faster direct routes to reach these safer prey. The Los Baños P. labiata apparently makes risk-related adjustments specific to whether scytodids are carrying eggs, but P. labiata from Sagada in the Philippines (allopatric to Scytodes) fails to make comparable risk-related adjustments.