Like ecstatic fans at a baseball game, fiddler crabs (Uca annulipes) do the wave. To attract sparse females (right), small male scuttlers (left) gather in large clumps, frantically shaking their oversized claws—similar to the novelty foam fingers popular at sporting events. But when competition between studs peaks, these spurts of friendly greetings can turn into downright wave-a-thons, a new study suggests. Males tend to wave enthusiastically in big crowds, presumably to stand out from their rivals, but they slow their gesticulating by about 30% when alone, researchers report online today in Biology Letters. Big waves nab females, but they can come at a price: The exertion saps a fiddler crab's energy and can catch the eye of predators, such as small shorebirds like rust-colored ruddy turnstones. Still, it could be worse: Unlike South African soccer fans, these beach invertebrates have yet to discover vuvuzelas.

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