-- Mary Elizabeth Dallas
THURSDAY, Feb. 9 (HealthDay News) -- Zebras evolved from all
black to striped in order to repel insects that distract them from
feeding, a new study contends.
Researchers from Hungary and Sweden said that zebras' black and
white stripes are the least-attractive hide pattern to
disease-carrying bloodsuckers known as tabanids or more commonly,
The researchers found that horseflies are drawn to horizontally
polarized light resembling reflections from water. They explained
that this is how insects find areas of water where they can lay
their eggs. Female horseflies also use the light reflected from
animals' hides, particularly black hides, to detect their victims,
the study noted.
The study, published online in the March issue of the
Journal of Experimental Biology, pointed out that as embryos, zebras start out with dark skin. They go on to develop their white stripes before birth. The researchers suggested this was an evolutionary adaptation to help them avoid bug bites.
The researchers tested their theory at a horse farm near
Budapest that was infested with horse flies. They altered the
width, angle and density of the stripes and changed the direction
of polarization of the light they reflected. Using oil and glue,
they trapped the insects to reveal which pattern attracted the most
The study showed the narrower the stripes, the fewer flies they
attracted. The researchers also tested the attractiveness of a
white, dark and striped horse. The study found the striped horse
drew the least flies.
"We conclude that zebras have evolved a coat pattern in which the stripes are narrow enough to ensure minimum attractiveness to tabanid flies," the researchers wrote in a journal news release.
The University of Kentucky College of Agriculture provides more
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