The hunting and feeding behaviour of the jumping spider Phidippus audax was examined in the laboratory under single and multi-prey conditions. When given the choice, spiders consistently selected insects with high activity levels and crawling velocities. Selection was not correlated with insect length, mass, or length/width ratio. However, cine analysis of single predator-prey encounters indicated that, at the time of detection, prey size (length and mass) was evaluated by the predator; spiders pursued large insects at significantly slower rates (i.e. more cautiously) than small insects. Prey size also significantly affected handling times. Time invested in handling preferred items was similar whether these were encountered alone or with alternate prey available. However, as predicted by the optimal foraging theory, spiders spent significantly less time feeding on lower ranked items in the presence of alternative prey.