Who Knew This Is Why Zebras Have Such Striking Coloration?

Zebra Stripes

Story at-a-glance -

  • Why do zebras have stripes? This riddle has puzzled researchers and animal experts for centuries. But a team from the University of California, Davis may have discovered the answer.
  • The team tested data collected on several different species and subspecies of zebras and other African hooved mammals against five common theories for why zebras have stripes. Based on their evaluation, they were able to rule out all but one theory.
  • In a study published recently in Nature Communications, the UC-Davis team revealed that the most logical explanation for zebra stripes is that they serve as a deterrent for biting flies, which are known to avoid black-and-white striped surfaces.
  • Another revelation from the study is that it is likely stripes evolved to compensate for unusually short body hair that does not protect zebras against the bites of tsetse flies and horseflies.
  • Biting flies tend to harbor a number of infectious diseases, and they have voracious appetites. In a study of cows and horseflies in the U.S., the cows lost up to a pint of blood a day to the flies, and up to 40 pounds of weight over an 8-week period.

By Dr. Becker

The purpose of the zebra’s black and white stripes has mystified scientists and laymen alike for centuries.

But now a research team from the University of California-Davis has taken a different approach to solving the riddle of the stripes, and their explanation was recently revealed in the journal Nature Communications.1

Researchers Tested 5 Theories for Why Zebras Have Stripes

Theories for the stripes that have surfaced over the years include:

  • They are a method of camouflage.
  • They are defensive weapons to visually confuse predators.
  • They help regulate the zebra’s body temperature.
  • They deter ectoparasites (biting flies), as earlier research has shown that the flies tend to avoid black-and-white striped surfaces.
  • They serve some sort of social function for the zebras

The UC-Davis team gathered information on different species and subspecies of zebras and other striped African hooved mammals, measured their data against the five theories, and ruled out all but one. They determined it is likely that biting flies such as tsetse flies and horseflies are the reason for zebra stripes, because their data showed greater striping on the animals living in parts of the world where biting flies are abundant.

Africa is well known for having a wide distribution of tsetse flies, but no such information exists for horseflies or deer flies. So the UC-Davis team mapped locations that would theoretically provide the best breeding conditions for those flies, and discovered that striping on zebras is closely linked with several consecutive months of excellent conditions for horsefly reproduction.2

Zebra Stripes May Have Evolved to Compensate for Unusually Short Body Hair

According to lead study author Tim Caro, professor of wildlife biology at UC-Davis:

“No one knew why zebras have such striking coloration. But solving evolutionary conundrums increases our knowledge of the natural world and may spark greater commitment to conserving it.”

Interestingly, the UC-Davis researchers might have uncovered another intriguing detail about zebras. It seems that unlike other hooved animals native to Africa, zebras have body hair that is shorter than the mouthpart length of biting flies, which would make them particularly vulnerable to the flies. So the stripes may have evolved as a deterrent.

Parasitic flies can carry a long list of diseases they transmit when they attach to a new host. Studies on horseflies in the U.S. suggest that cows can lose over a pint of blood a day to the flies, and up to 40 pounds of weight over eight weeks.