Grey horses are more fly-repellent, research suggests

Although grey horses may look striking, they apparently aren’t too tasty to blood-sucking flies.

A recent study by a group of researchers from Hungary, Spain and Sweden suggests that grey horses are less attractive to disease-spreading tabanid flies than black or bay horses.

So although lighter horses may be more sensitive to ultraviolet solar radiation — that can lead to skin cancer and deficiencies of the visual system — there might be less chance of them being bitten — thus avoiding disease.

The study “An unexpected advantage of whiteness in horses: the most horsefly-proof horse has a depolarising white coat,” says flies find grey horses less attractive because their colour absorbs more light than bays.

“We demonstrate that tabanids use reflected polarised light from the coat as a signal to find a host,” the study states.

But H&H vet Karen Coumbe is sceptical. “In my experience there is nothing to say whether flies are attracted more to one colour than another,” she said.

“Some horses are more susceptible to flies than others but I’m not convinced it’s related to colour. I would have thought it was more about how hot, sweaty and grubby the horse was.”

This article was first published in Horse & Hound (18 March, ’10)

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