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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Coronavirus dashboard

Illustration: Sarah Grillo/Axios

  1. Global: Total confirmed cases as of 11 p.m. ET: 721,817 — Total deaths: 33,968 — Total recoveries: 151,204.
  2. U.S.: Leads the world in cases. Total confirmed cases as of 11 p.m. ET: 142,328 — Total deaths: 2,489 — Total recoveries: 4,767.
  3. Federal government latest: President Trump says his administration will extend its "15 Days to Slow the Spread" guidelines until April 30.
  4. Public health updates: Fauci says 100,000 to 200,000 Americans could die from virus.
  5. State updates: Louisiana governor says state is on track to exceed ventilator capacity by end of this week — Cuomo says Trump's mandatory quarantine comments "panicked" some people into fleeing New York
  6. World updates: Italy on Sunday reports 756 new deaths, bringing its total 10,779. Spain reports almost 840 dead, another new daily record that bring its total to over 6,500.
  7. What should I do? Answers about the virus from Axios expertsWhat to know about social distancingQ&A: Minimizing your coronavirus risk
  8. Other resources: CDC on how to avoid the virus, what to do if you get it.

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Data: The Center for Systems Science and Engineering at Johns Hopkins; Map: Andrew Witherspoon/Axios

The novel coronavirus has now infected over 142,000 people in the U.S. — more than any other country in the world, per Johns Hopkins data.

The big picture: COVID-19 had killed over 2,400 people in the U.S. by Sunday night. That's far fewer than in Italy, where over 10,000 people have died — accounting for a third of the global death toll. The number of people who've recovered from the virus in the U.S. exceeded 2,600 Sunday evening.

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There are now more than 720,000 confirmed cases of the coronavirus around the world, according to data from Johns Hopkins. The virus has now killed more than 33,000 people — with Italy alone reporting over 10,000 deaths.

The big picture: Governments around the world have stepped up public health and economic measures to stop the spread of the virus and soften the financial impact. In the U.S., now the site of the largest outbreak in the world, President Trump said Sunday that his administration will extend its "15 Days to Slow the Spread" guidelines until April 30.

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