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Why Do Cows Have Spots?

Cows’ mottled coats may have evolved to help keep flies away.

Longhorn cattle in Houston, Texas. (

Animals come with a wide variety of spots, colors, stripes and patterns. For each of these adaptations, there is certainly a reason, right? Maybe it’s for camouflage, or maybe they just want to look sexy for their friends.

Zen Faulkes, an evolutionary biologist at the University of Texan-Pan American, highlights a new idea for spots’ apparent purpose: bug repellant. In cows, at least, a mottled coat can trick horseflies into pestering someone else, says Faulkes says Faulkes.

Referencing two different studies, one looking at zebras and another for cows, Faulkes says that a cow’s spotted coat can confuse a horsefly’s vision, which is tuned to see polarized light. The dark and light spots of some cows change how polarized light is reflected.

The authors of the study on cows found “that the smaller and the more numerous the spots, the less attractive the target is to tabanids .”

This could be one of the possible evolutionary benefits that explains why spotty coat patterns are so widespread in mammals, especially in ungulates, many species of which are tabanid hosts.

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About Colin Schultz
Colin Schultz

Colin Schultz is a freelance science writer and editor based in Toronto, Canada. He blogs for Smart News and contributes to the American Geophysical Union. He has a B.Sc. in physical science and philosophy, and a M.A. in journalism.

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