The oldest argument in the field
Why Do Zebras Have Stripes?
People have argued about zebra stripes for a hundred and fifty years. The best answer turned out to involve flies.
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Step 1 of 5
It is not hiding from lions.
A zebra on open grass is one of the most obvious animals there. Lions catch zebras perfectly well, and lions see poorly in colour anyway, so hiding cannot be the main reason.
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Step 2 of 5
Flies cannot land on stripes.
Biting flies steer by watching a surface swell as they approach. Strong stripes wreck that signal, and researchers filmed flies bumping into striped horses and veering away instead of landing.
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Step 3 of 5
The test was a coat.
Scientists put striped coats on ordinary horses. Flies landed far less on the striped ones than on the same horses in plain coats — the animal had not changed, only the pattern.
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Step 4 of 5
A herd becomes one moving mass.
When hundreds of striped animals run together the edges of individuals blur into each other. Picking one target out of that and staying locked on it is genuinely harder.
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Step 5 of 5
Every pattern is one of a kind.
A foal learns its mother's stripes in the first days and follows that pattern in a crowd. Mothers keep newborns away from the herd at first so the pattern is learnt cleanly.
A zebra is black with white stripes, not the other way round. The skin underneath is black all over.
The short version
Zebra stripes mostly seem to defeat biting flies, and they blur one animal into the herd when it runs.
Try it yourself
Look at a strongly striped shirt while someone walks towards you. Judging exactly how far away it is takes a moment longer.