Explanations for why zebras are stripey run a wide gamut: some say camouflage, or that it makes it hard to target individual members of the herd, or even that it's a cooling method. Well, add another one to the list, which at least has some experimentation behind it.
New research published in the Journal of Experimental Biology looked at how differences in skin tone effected the attractiveness of animals to blood-sucking horseflies. They already knew that dark skinned horses tend to get bitten far worse than white, so they wondered if the zebras had evolved stripes as a way of mitigating that.
As an aside, apparently zebra embryos start dark and then grow white stripes, finally solving the whole "white with black stripes" or "black with white stripes" debate.
The researchers looked at varying angles, widths, and density of the stripes, and found the smaller and closer packed the color changes, the less the horseflies were interested. In fact, the striped models were less attractive to the insects than either solid color. Couple this with the fact that zebras also reflect light at a polarity that the bug dislikes, and you have an effective measure for combatting being bitten.
As the researchers commented:
"We conclude that zebras have evolved a coat pattern in which the stripes are narrow enough to ensure minimum attractiveness to [horseflies]. The selection pressure for striped coat patterns as a response to blood-sucking dipteran parasites is probably high in this region [Africa]".
It is entirely possible that the stripes evolved as a combination response to a variety of population pressures, but this certainly puts a new spin on an old story.
Image by Anna-Carin Bäckman