Visual ecology of biting flies.

Many of the similarities in visual ecology between the Nematocera and Brachycera and within the Cyclorrhapha may reflect the evolution of blood-feeding in these groups. In Nematocera and Brachycera, blood-feeding is thought to have evolved from predatory or nectar-feeding behavior (138). Only females feed on hosts, and association with hosts generally occurs when hosts are close to the aquatic or semiaquatic habitats of the immatures. Flies feed on nectar, make appetitive flights, disperse, or migrate prior to blood-feeding, and then oviposit in water. Many species are nocturnal or crepuscular. In Cyclorrhapha, flies are closely associated with hosts. They may have arisen from compost-feeding flies that developed a larval dependence on vertebrate-produced microhabitats. Both sexes blood-feed, and mating occurs on or near hosts. Flies generally emerge in the proximity of hosts and maintain close contact with them. These species are diurnal, and their visual systems are well developed. Comparisons between closely related blood-feeding and non-blood-feeding species may provide insight into the visual ecology of blood-feeding species. Despite the different origins of hematophagy, there appears to be a convergence of morphology and behavior that is related to ecology rather than to phylogenetic relationships. This is clearly seen in host-location strategies by tsetse and tabanids. Even within groups such as mosquitoes, species that are active at the same time of day and in the same habitat have more in common than closely related species in different habitats. For this reason, an ecological review would be more cohesive than this phylogenetic discussion. However, because of the disproportionate amount of literature on a small number of groups, the phylogenetic approach is the most practical for this subject. However, this review does point out the great need for research on the less well-studied groups and behaviors.