June 27, 2023
Spots or Stripes This Season?
- as seen by -Natalie Ingle
A group of zebra are called a dazzle for obvious reasons. Less obvious may be the fact that their stripes are more useful for confusing miniature pests than they are for disorienting would-be predators. It turns out that the strongest theory to date for why zebra evolved black and white coats in a green and gold world is the deterrent effect the stripes have on biting flies.
In numerous experiments, including this one reported in the journal Plos One, scientists have shown that, while flies will approach a zebra as much as any other grazer, they somehow fail to actually land on the zebra—zooming over or literally bumping into them. The same effect has never been proven with lions or hyenas, unfortunately for the zebra.
Given that parasitic flies carry a host of diseases, it’s easy to see why a trick like this would be an evolutionary advantage. In Niassa Special Reserve, which the Wildlife Conservation Society co-manages with the Mozambican government, for example, the presence of tsetse flies has greatly suppressed the local economy’s reliance on livestock because the flies carry Trypanosoma vivax which can be devastating for cattle and other hoofstock.
In Rwanda’s Akagera National Park, which is in my own backyard, tsetse flies are primarily just an annoyance. Royal blue and black flag traps, which are thought to mimic the shady underbellies of their victims, are soaked in insecticide to catch and monitor flies for disease. However, they don’t do much to stop swarms of the insects from harassing anything that moves, including vehicles. But zebra do just fine both here and in Niassa.
Humans have not yet evolved a natural deterrent to avoid their painful bites and, it seems, spots don’t work either. Look closely and you can even see the pint-sized pest that just bit this leopard (above).