Zebra stripes may 'dazzle' pathogen-packing horse flies, say scientists

Saturday, February 23, 2019

In findings published on Wednesday in PLoS One, scientists from the University of Bristol and UC Davis say zebras may have gotten their stripes to confuse ectoparasites, such as flies.

A Grevy's Zebra (Equus grevy)
Image: André Karwath aka Aka.

The researchers observed tabanid horse flies around zebras and domestic horses in captive settings and they found the flies had a harder time landing on zebras than on the monochrome coats of the horses.

Results showed the horse flies hovered over both types of animals at roughly the same rate but, over zebras, they did not always slow down fast enough to land successfully. They then equipped horses with both zebra-striped and unstriped cloths and again observed that the flies had trouble landing on the striped surfaces.

"This reduced ability to land on the zebra's coat may be due to stripes disrupting the visual system of the horse flies during their final moments of approach. Stripes may dazzle flies in some way once they are close enough to see them with their low-resolution eyes[,]" said study co-author and Royal Society University Research Fellow Martin How.

A horse fly.
Image: Benjamint444.

Scientists have long wondered about the evolutionary impetus behind zebras' coat patterns. Other hypotheses include the idea that stripes may confuse predators, facilitate social interactions within the herd, and regulate body temperature.

In Africa, where zebras evolved, flies can carry dangerous blood-borne pathogens.