Why Zebra Stripes Confuse Flies

The best-supported answer to a 150-year argument is not lions. It is horseflies.

Darwin and Wallace argued about zebra stripes and the argument ran for a century and a half: camouflage, cooling, social recognition, predator dazzle. The experiments finally caught up, and the strongest evidence points somewhere unglamorous — biting flies. Horseflies approach striped surfaces at speed and fail to decelerate properly, bouncing off or aborting the landing entirely.

Researchers dressed horses in striped coats and counted landings: dramatically fewer on the stripes than on plain coats, same horse, same field. The flies carry diseases that kill equids in Africa, so a coat that breaks their landing approach is worth real fitness.

The dazzle-the-lion theory, for the record, failed its tests — lions catch zebras just fine. Nature’s boldest pattern seems to exist for an enemy a centimetre long.