Zebra Stripes as Bug Repellant
On the plains of Africa, the zebra are not the only creature roaming in herds. There are a great number of other species, not least of all, the dreaded horsefly. Zebras, like all horse species, have large bodies which they cannot always reach with their mouths, hooves, or tails, making them an inviting prey for blood-sucking, flying insects. More than the lion, the horsefly is the bane of zebra's existence. This, according to a recent study published in the Journal of Experimental Biology, is why zebras evolved to having stripes. The black and white stripes effectively deter the horseflies by making the zebras less attractive.
The horsefly, part of the Tabanidae family, is the largest of all flies. They are very loud and their bites can be painful. The fly is fast and agile, make it extremely difficult to swat.
Their razor sharp mandibles slice the flesh apart, allowing the female horsefly to nourish itself on blood, which is necessary for their reproduction. The bites often become very itchy, causing great discomfort and distraction to the grazing herbivore. Horseflies are also vectors for blood-borne pathogens including the equine infectious anaemia virus, parasitic filarial worm, and even anthrax.
If the animal is attacked by a swarm of horseflies, it is possible that the animal can lose up to 300 milliliters of blood in a day, weakening it and potentially cause death from blood loss.
The study was conducted by Gábor Horváth, Susanne Åkesson, and colleagues from Hungary and Sweden. They looked at the behavior of horseflies at a horse farm near the city of Budapest.
Using alternating black and white stripes of various widths, densities, and angles, light reflections, they set the trap. Oil was spread over the stripes to attract the flies and glue was spread to snare them.
They found that fewer flies were attracted as the stripes became narrower. The narrowest stripes attracted the least amount of horseflies.
'We conclude that zebras have evolved a coat pattern in which the stripes are narrow enough to ensure minimum attractiveness to tabanid flies', says the team and they add, 'The selection pressure for striped coat patterns as a response to blood-sucking dipteran parasites is probably high in this region [Africa]'.
The researchers found that the flies are attracted more to dark hides than to white hides. However, they are attracted least of all to striped hides. This can explain a great deal of how the zebra got its stripes. In fact, a zebra fetus while it is in the womb has dark skin. It then develops stripes just before being born, protecting it from the vicious appetite of the dreaded horsefly.
Zebra image via Shutterstock