Biting flies and zebra stripes

In all probability, biting flies are the evolutionary force that has shaped the extraordinary coat colouration of the zebra, but there are a number of questions raised by this contention, which we address in this review. We divide our discussion into: (1) which groups of biting flies are thwarted by contrasting black and white striping; (2) the variety of ways in which stripes might interfere with normal landing behaviour of flies; (3) the ecological assumptions underlying fly-zebra sympatry; and (4) the zebra diseases for which flies are vectors. We note that tabanid species differ in their landing sites on equids, and that glossinids may not be affected by the stripes in the same ways as tabanids. We argue that disruption of optic flow is a possible candidate for thwarting tabanid landing behaviour but current evidence speaks against this and in favour of sudden target disruption. We show that tabanid and glossinid distributions closely overlap those of zebra species, at a geographic and microhabitat scale, and that flies can carry several diseases fatal to zebras. We suggest that future research be targeted at the mechanism by which stripes thwart proper landing performance and identify which diseases and which carriers most impact zebras.