Scientists have long been intrigued by the striking black and white stripes of zebras. For years, the prevailing theory suggested these stripes served as camouflage, disrupting predators’ vision. However, recent research has unveiled a different primary function: deterring biting flies. But how exactly do these stripes achieve this fly-repelling feat? A new study delves deeper into the visual interaction between flies and zebras, particularly exploring how stripes, and by extension the color white, might confuse these persistent pests.
Researchers from the University of California, Davis, and the University of Bristol, led by Professor Tim Caro and Martin How, conducted a series of experiments to understand how stripes affect biting flies attempting to land on zebras. Their work, published in PLOS ONE, involved detailed observations and video analysis on a UK horse farm housing both zebras and horses. The team meticulously recorded fly behavior around zebras, capturing flight paths with high-definition cameras. To isolate the effect of stripes, they even dressed both horses and zebras in coats of solid black, solid white, and, of course, black and white stripes.
Stripes: A Visual Puzzle for Flies
The study revealed a fascinating insight: flies are equally attracted to zebras and horses from a distance. This indicates that zebra stripes don’t act as a general repellent. The magic happens when flies get close. “Once they get close to the zebras, however, they tend to fly past or bump into them,” explains Caro. “This suggests that stripes interfere with the flies’ ability to execute a controlled landing.”
Intriguingly, when comparing fly landings on different colored coats, the striped coats saw significantly fewer landings than both the black and white coats. This is where the question “Can Flies See White?” becomes particularly relevant. While flies are attracted to dark colors, possibly due to heat signatures or visual contrast against the sky, the white stripes might be playing a crucial role in disrupting their vision upon close approach.
How suggests that the stripes might “dazzle flies” once they are within close visual range. This “dazzle” effect likely stems from the low-resolution eyes of flies. Imagine looking at a rapidly moving striped pattern with blurry vision – the contrasting black and white lines could create a confusing visual input, making it difficult to judge distance and trajectory accurately for landing. The color white, being highly reflective, could exacerbate this effect by creating strong visual flicker and further disrupting the fly’s visual processing.
Zebra Defenses Beyond Stripes
Beyond their confusing stripes, zebras possess behavioral defenses against flies that differ markedly from horses. Zebras are relentless tail-swishers, constantly working to dislodge flies. They are also quick to stop feeding and even run away if flies become too bothersome. Horses, in contrast, mainly rely on skin twitching and occasional tail swishes. This more active defense mechanism in zebras further contributes to their ability to minimize fly landings and bites. Any fly that does manage to land on a zebra is quickly dealt with, unlike on horses.
The evolutionary reasons behind these sophisticated zebra defenses remain a topic of ongoing research. One compelling hypothesis links it to disease. African biting flies are vectors for numerous infectious diseases. Zebras, potentially being highly susceptible to these diseases, may have evolved both visual and behavioral strategies to minimize fly contact as a matter of survival. Further studies are needed to fully unravel this complex interplay between zebra stripes, fly vision, and evolutionary pressures.
References:
- How, M. J., Caro, T., et al. (2019). Stripes Break Flies: Zebra Stripes and Biting Flies. PLOS ONE, 14(2), e0210831.
