Spiders do not feed directly on vertebrate blood, but a small East African jumping spider (Salticidae), Evarcha culicivora, feeds indirectly on vertebrate blood by choosing as preferred prey female mosquitoes that have had recent blood meals. Experiments show that this spider can identify its preferred prey by sight alone and by odor alone. When presented with two types of size-matched motionless lures, E. culicivora consistently chose blood-fed female mosquitoes in preference to nonmosquito prey, male mosquitoes, and sugar-fed female mosquitoes (i.e., females that had not been feeding on blood). When the choice was between mosquitoes of different sizes (both blood- or both sugar-fed), small juveniles chose the smaller prey, whereas adults and larger juveniles chose the larger prey. However, preference for blood took precedence over preference for size (i.e., to get a blood meal, small individuals took prey that were larger than the preferred size, and larger individuals took prey that were smaller than the preferred size). When presented with odor from two prey types, E. culicivora approached the odor from blood-fed female mosquitoes significantly more often the odor of the prey that were not carrying blood.