Zebras evolved their stripes to avoid disease-spreading biting flies rather than to confuse predators, a study suggests.
The black and white stripes deter tsetse flies and horseflies by interfering with their visual homing system, scientists believe.
How the zebra got its stripes has been a long-standing riddle not even solved in Rudyard Kipling’s famous Just So stories. Leading theories have involved camouflage, tricking predators into misjudging the speed or size of their prey, reducing overheating, and social behaviour.
Previous research has also suggested protection against biting flies. Horseflies, for instance, are less likely to land on a black and white surface than a monochrome one. Tsetse flies have also been shown to avoid stripes.
For the new study, a team of US scientists looked at the regional distribution of seven different species of zebras, wild horses and asses, some of which are striped and some not.
They then compared the animals’ geographic ranges with a number of variables including woodland areas, predator territories, temperature, and the presence or absence of tsetse flies and tabanids, or horseflies.
Only the distribution of striped species was firmly linked to the biting insects.
“I was amazed by our results,” said lead scientist Tim Caro, from the University of California at Davis. “Again and again, there was greater striping on areas of the body in those parts of the world where there was more annoyance from biting flies.
“No one knew why zebras have such striking colouration. But solving evolutionary conundrums increases our knowledge of the natural world and may spark greater commitment to conserving it.”
Again and again, there was greater striping on areas of the body in those parts of the world where there was more annoyance from biting flies
Zebras may have evolved their striking stripes because they are especially sensitive to biting flies, the scientists believe. Unlike other African hoofed animals, their hair is shorter than the length of the insects’ mouth-parts.
The researchers wrote in the journal Nature Communications: “Our results lend strong ecological and comparative support to experiments that show that some tsetse and tabanid species avoid black and white striped surfaces.
“Biting flies are attracted to hosts by odour, temperature, vision and movement that may act at different stages during host seeking, but vision is thought to be important in the landing response.”