Arthropod-transmitted parasites can enhance their transmission by modifying vector blood-feeding behavior. Malaria sporozoites invade specific regions of mosquito salivary glands, where they cause a loss in apyrase levels, an antiplatelet aggregation enzyme that enhances blood location by probing mosquitoes. As a consequence, infected mosquitoes probe longer and contact more hosts to which they can transmit the pathogen than do uninfected mosquitoes. In vertebrate hosts, blood-borne parasites induce hemostatic changes so that mosquitoes locate blood faster in infected hosts than in uninfected hosts. These modifications in vector-host interactions may force us to reevaluate the vectorial capacity of mosquitoes.