Scientists Discover Why Biting Flies Are Attracted to Blue

Daytime biting flies misclassify blue objects as animals
By Rob Quinn,  Newser Staff
Posted Jul 2, 2023 10:15 AM CDT
Here's Why Biting Flies Like Blue
We don't know this horse fly's star sign, but its favorite color is blue.   (Getty Images/Ilya Starikov)

Bluebirds, blue-tailed skinks, blue whales, and Babe the Big Blue Ox aside, blue animals are rare in nature, but biting flies still associate the color with food, researchers say. Lead researcher Roger Santer from Aberystwyth University in Wales says entomologists have long known that biting flies active in the daytime, including tsetse flies and horse flies, are attracted to blue but it was unclear why, the Guardian reports. Some believed the flies associated the color with shady areas; others thought the flies might be drawn to bodies of water or that the preference for blue was a "by-product of attraction to polarized light," researchers say.

In research published in Proceedings of the Royal Society B, Santer and his fellow researchers say they trained artificial neural networks—simulations of the brains of common biting flies—using the five types of photoreceptor in a fly's eye. They found that the networks never mistook the color blue for shade, but they often misclassified blue objects as animals to feed on, probably as a result of using blue-green opponency in photoreceptors as a way of distinguishing animals from leaf matter. Researchers also noted that flies caught in blue traps in field experiments were "relatively starved, indicating that they were seeking hosts."

Blue is already commonly used in traps for biting flies and the team hopes the study will help build better flytraps. "If we can understand the mechanisms that attract flies to colored traps, we can improve the color of those traps so that they more efficiently catch flies," Santer says, per the Guardian. "This is a really important aim because different species of biting flies spread diseases of humans and animals, so fly control is an important part of disease control." (More flies stories.)

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