The Unexpected Reason Scientists Painted A Cow Like A Zebra

In 2019, a team of Japanese scientists did something bold, brilliant, and bizarre: they painted a cow like a zebra. Actually, they painted six cows like zebras, applying a pattern of stripes to half a dozen Japanese black cows at the Aichi Agricultural Research Center in Nagakute. What on Earth would possess someone to paint livestock like so? It was all done in the name of pest control.

Biting flies are a scourge to cattle, and by proxy, farmers. These tiny pests feed on the blood of livestock, causing painful swelling and lesions. They disrupt the sleeping and feeding schedules of cows, which can lead to weight loss. In the most serious cases, biting flies can spread diseases, and, if they attack en masse, can even kill cattle through blood loss. The most common way to deal with biting flies is by using chemical pesticides, often applied directly to cows themselves, but these pose significant environmental risks.

The team of scientists in Japan believed there had to be a better way to keep flies away from cows, and for inspiration, they looked to zebras. The most notable characteristics of zebras are their stripes, which are thought to have evolved, at least in part, to deter biting flies. The team hypothesized that painting zebra stripes on other animals could effectively keep away biting flies. They put this to the test, and publishing in the journal PLOS One, found that painting stripes on cows caused biting flies to land half as often.

To put their theory to the test, the scientists studied six Japanese black cows, which, as their name suggests, are naturally black in color. Researchers observed all six of the cows in this natural state to provide a control, an important part of the scientific method. They also observed all six cows with two different patterns applied: a coat of all black stripes, and a coat of black and white stripes. The stripes were all made with waterborne lacquer.

When the cows were painted black and white, like a zebra, they showed a 50% reduction in biting flies landing on them versus when they were painted with all black stripes or in their natural, all-black coats. When painted like zebras, the cattle showed a significant reduction in fly-repelling behaviors such as stomping, tail flicking, and head shaking, appearing noticeably more comfortable. This suggests that painting livestock like zebras is actually an effective pest repellant.

Scientists believe that zebra stripes are an effective deterrent because of the way that flies' compound eyes function. They process images faster than human eyes, but at a lower resolution. Zebra stripes may create an optical illusion for flies that make it appear as if the animal is moving, making it very hard for the fly to time a landing. Other studies have shown that painting zebra stripes on objects and furniture can repel flies, but this is the first time anyone has put it to the test on livestock.