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'Disco clam' lights up to scare predators away

WEST PALM BEACH, FLORIDA—The bright,  orange-lipped “disco clam” (Ctenoides ales) became a phenom last year when researchers learned that its dazzling display (see video above) proved to be reflections of ambient light and not light produced by the clams themselves. Now that same team has strong evidence that these blinking streaks are telling would-be predators, "Beware!" When the researchers conducted their initial study, they thought perhaps the flashes were used to lure in other clams. But young clams show no preference for the light show; indeed, their 40 eyes fail to respond at all to these lights. Instead, the flashes do seem to help the clam avoid being eaten. The clams, which live off Indonesia, flash twice as much when they spot predators. And when a peacock mantis shrimp attacks one of these 6-centimeter-long clams, the shrimp quickly recoils as if stung or tasting something really terrible, the researchers reported here today at the annual meeting of the Society for Integrative and Comparative Biology. They found that the clam has sulfur in its fleshy lips and tentacles and suspect that, like another clam species that drop tentacles laden with sulfuric acid to deter predators, the disco clam's sulfur also gets converted into a distasteful substance. The flashing may warn predators away, similar to the bright orange of a monarch butterfly warning birds of its toxic taste.

(Main video credit: Lindsey Dougherty; linked video credit: Roy Caldwell, University of California, Berkeley)