Scientists Reexamine Why Zebra Stripes Mysteriously Repel Flies

Arthur T Knackerbracket writes:

https://www.wired.com/story/scientists-reexamine-why-zebra-stripes-mysteriously-repel-flies/

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.

Writing in Scientific Reports this month, they describe how their experiment in Kenya led to two discoveries that buck some previous theories. Tombak's team agrees there is an illusion-but since they restricted the flies to a 4-foot-wide box, they argue that the mechanism happens up close, not from afar. They also found that narrow zebra stripes don't repel flies any better than wider ones. "That was a surprise because previous studies had indicated that there might be a difference," says Tombak, who is currently a postdoctoral researcher at Hunter College.

[...] For the current study, Tombak, then a PhD candidate at Princeton, and her team wanted to test stripe width to see if narrower ones might be even more repulsive to flies-a potential evolutionary advantage that would explain the difference between zebra species. They also restricted their experiment to close-range encounters to rule out the theory that the repulsion required an illusion that could only happen at a distance. Hence the plexiglass box.

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