Zebra stripes appear to create optical illusions for horseflies and might cause them to avoid approaching altogether. | Photo: iStock

It appears, however, that researchers have eliminated one hypothesis from the list of possibilities: They recently determined that it’s unlikely that polarization is what confuses flies, said Kenneth Britten, PhD, of the Department of Neurobiology, Physiology, and Behavior at the University of California, Davis (UC Davis).

Polarization is a physics concept that—very simply put—describes the way the electric vectors in light waves move in certain distinct patterns. While humans can’t detect that polarization, horseflies (“tabanids”) can. Considered “polarotactic,” horseflies are very attracted to certain kinds of polarization. The horizontal polarization of water-reflected light, for example, leads them to water sources where they can mate, reproduce, and rehydrate. Linear polarization leads blood-sucking female horseflies to food sources such as equids and cattle.

For years, many researchers believed zebra stripes affected light polarization in a way that repelled flies. But scientists are now shedding a new angle of light on that theory