Feb 21, 2019

Zebra stripes confuse biting flies


Joren Bruggink and Jai Lake investigate how horse flies behave around horses wearing different colored coats. Photo: Tim Caro/UC Davis

The next time you're looking to avoid getting bit by flies, you might want to try putting on zebra-patterned clothing.

Why it matters: A study published Feb. 20 in the journal PLOS ONE helps explain why zebras, with their prominent stripes, don't get bit by many horseflies. It sheds further light on a mystery that has puzzled scientists for more than a century: How did zebras get their stripes?

Tim Caro, a wildlife biologist at the University of California, Davis, and Martin How of the University of Bristol led experiments on a horse farm in Britain to observe flies' attempts to land on zebras and horses.

Background: Caro's previous research has shown that zebras are found in regions where biting flies are common and their stripes likely serve as a deterrent. The new study investigates how flies are affected by such stripes.

What they did: The scientists recorded close-up videos to determine flight trajectories as flies closed in on their targets. They also dressed the horses and zebras in black and white, as well as black-and-white striped coats, to see how the patterns and colors affected the flies' flight paths.

What they found: The study shows that the zebra stripes did not deter flies from trying to land on zebras when compared to horses. However, they saw far fewer touches and landings from biting flies, which can spread disease, than bare horses did.

  • Video analysis showed that horse flies approached zebras at faster speeds and failed to decelerate before hitting their skin. Proportionately, more horse flies hit zebras and simply bounced off when compared to horse fly approaches to horses, which involved more successful landings and bites.
  • The horses cloaked in stripes saw fewer fly landings on the striped portions, but there were no differences in landings and bites to their bare heads.

What they're saying: “Stripes may dazzle flies in some way once they are close enough to see them with their low-resolution eyes,” How said in a press release.

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