Horseflies, the females of which feed on blood, are attracted to polarized light—light waves that are oriented in a particular direction and that we experience as glare. This glare lures the bugs most likely because it resembles light reflected off water, where they lay their eggs.

On horses, black fur reflects polarized light better than brown or white, as evolutionary ecologist Susanne Åkesson and colleagues found in a previous study.

The researchers therefore assumed that zebra coats, with their mixtures of light and dark stripes, would be less attractive to flies than those of black horses but more than those of white horses.

But after experiments in which they team measured the number of horseflies that became trapped on gluey, striped