Scientists Reexamine Why Zebra Stripes Mysteriously Repel Flies
Biologists still aren't exactly sure how it works
Approximately 30 miles north of the equator, in central Kenya, Kaia Tombak and her colleagues stood beside a plexiglass box. Tombak, who studies the evolution of animals’ social behavior, was dressed for the power of the Savannah sun in a light, long-sleeved shirt and pants. A gang of flies buzzed nearby, and Tombak wondered whether she would be better off wearing stripes.
That was why her team was here: to study the fly-repelling power of stripes. Inside the box hung two foot-wide pelts from carcasses found nearby. One was from a tan impala. The other was from a zebra. In between the two was a petri dish trapping 20 or so flies. A teammate tugged on a fishing line, yanking the dish open. The flies scattered and found new landing spots within seconds. To nobody's surprise, they avoided the zebra pelt. "It really does work," said Tombak.
Biting flies slurp their meals from the blood of Savannah animals. At best, the flies are annoying. At worst, they transmit disease. Scientists have known since the 1980s that zebra stripes repel flies, and many believe that zebras evolved their distinctive stripes because of this advantage. But researchers still don’t actually know why the stripes work. Most theories suggest some visual illusion. Perhaps, up close, the stripes affect how biting flies perceive a zebra’s motion. Or from afar, stripes may scramble the outline of the animal’s body. For Tombak’s team, this raised an irresistible question about how a parasite, rather than food or mating strategies, could drive evolution.
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