The Secrets of the Toxic Disco Clam

Using the snotty strobe lights in its mouth, this deepwater mollusk can fend off hungry predators as mighty as the mantis shrimp.

The mantis shrimp is the undisputed lightweight champion of the sea. With a punch as fast as a .22 caliber bullet, the crustacean terrorizes small prey along the ocean floor. But now, an unexpected David has emerged from the depths to subdue this underwater Goliath: a toxic-snot-spewing mollusk with a Tesla-coil mouth.

Known as "the disco clam," this six-centimeter shellfish has tentacles that flash like a strobe light. At first, researchers thought the light was a type of bioluminescence like fireflies or deep-sea angler fish. But last year marine biologist Lindsey Dougherty from the University of California, Berkeley, found that the flashing lights are caused by highly reflective silica spheres in the clam’s bright orange lips. They initially thought the glow attracted mates, but now, new research from her team suggests that the light display may ward off would-be attackers.

In an experiment, Dougherty put a mantis shrimp in the same tank as a disco clam and monitored the animals’ activity. But as she quickly learned, the bivalve was not to be bullied. Once attacked by the shrimp, the clam spewed acidic mucus at the crustacean, disarming the shrimp and sending it into a catatonic state. Upon further investigation, Dougherty and her team found that the clam’s fleshy lips were laced with sulfuric acid, a substance commonly found in car batteries and drain decloggers. They reported their findings on January 4 at the annual Society for Integrative and Comparative Biology conference.

“If you're flashing and saying, ‘I'm distasteful; don't eat me,’ that's one thing, but you have to sort of back it up,” Dougherty said to Livescience. According to the researchers, mantis shrimps can crush a clamshell in just 45 seconds. But in the lab setting, the predator left the clam alone instead of devouring it. “That is very strange behavior [for the mantis shrimp],” Dougherty said. “They're very aggressive critters, and to have a clam open and flashing, and the mantis shrimp not attacking, is very weird.”

The team found that when a predator is present, the flamboyant fighter flashes its reflective lips at double its normal rate. For a prowling mantis shrimp, this may be one rave to avoid.