Scientists Paint Zebra-Like Stripes on Cows in an Attempt to Reduce Insecticide Use. It Worked Wonders

A few years back, farmers in Japan’s Yamagata prefecture were scared to release their Black cows into farmlands. The moment these cows would step outside, gangs of cattle flies or gadflies would swarm over their bodies, sting their soft flesh, and slurp in their blood. These bloodsucking insects make the cows restless with their constant buzzing and lead to their weight loss and sometimes disease. The plight of these farmers turned to relief when some researchers revealed that all it takes to shoo the flies away from cows, is a paint job. The trick, they said, to repel the annoying flies, is to confuse and disorient them by making them think that they’re seeing zebras, not cows. The findings of this research were published in the science journal PLOS ONE in 2019.

For cows, flies are a big nuisance, not just in Japan but everywhere. According to Purina Mills, a cattle feed manufacturing company, flies can extract up to 30 blood meals per day from a cow. Plus, as many as horn flies can make the slick oily hide of a cow their home, counting to as many as 120,000 bites per cow per day. The reason why flies are attracted to cows is their secretions including their manure, milk, tear fluid, and urine. Flies use these secretions as breeding grounds for their eggs and they may spend an entire life cycle breeding in it.

Not that these bites cause much irritation to the cows, but also lead to their weight loss and blood loss, which costs the cattle industry billions of dollars every year. And unlike humans who have hands to drive off flies, cows are helpless creatures. So while these parasitic vampires pierce their tentacles into the cow’s flesh, the cow stomps her hooves, wallows uneasily, gives out a painful moo, or tries to bunch together with her herd.

Scientists have known since the 1980s that zebra stripes repel flies. In the above-mentioned study, researchers carried out an experiment by recruiting six cows. They painted each cow with black-and-white stripes plus black stripes and no stripes. Then they monitored how flies reacted to the stripes and how many bites cows had to endure. They found that cows with no stripes or black stripes endured 110 bites in 30 minutes, whereas cows painted like zebras had to suffer fewer than 60, thus not requiring the use of insecticides on them.

“We found that painting zebra-like stripes on domesticated cows can decrease the incidence of biting flies landing on individuals by 50%,” the researchers reported in the conclusion. “We also found that the reduced landings of biting flies coincide with a reduction in defensive behaviors in cows,” they added. Although the method isn’t as efficient as ear tags or insect-repellent chemical spray, it offers some starting points on livestock pest control and environmental pesticide resistance.

The science of why these painted stripes work lies in the biology of a fly. WIRED explains that flies have “compound eyes” due to which their sense of color is very limited. While they can sense motion and polarized light, the images perceived by their eyes are very low resolution. Zebra stripes often confuse and disorient them, so they’re unable to decide the perfect landing spot, similar to the “barber pole illusion.”