Killer Shrimp.

Think WWF wrestlers use killer jabs? Meet the mantis shrimp. Commonly nicknamed "thumb splitter," this crustacean (animal with outer shell and segmented body) features club-like claws that spear and pulverize prey 50 times faster than the blink of your eye. Definitely not the specimen of choice for an aquarium. But two such unwelcome critters (Neogonodactylus curacaoensis) have slipped into a coral reef exhibit at the Monterey Bay Aquarium in California. Now they're smashing and dining on aquatic invertebrates (animals without backbones) like hermit crabs.

The three-inch-long shrimps--one dubbed "Sparky"--began their chomping spree last spring. "We could hear them snapping at the barnacles and noticed we were losing hermit crabs and snails," says senior aquarist David Cripe.

How did the killer shrimp invade the aquarium? In a crate of rocks from Florida, Cripe explains. Before aquarists place rocks into a display tank, they subject the rocks to a rigorous cleaning process called curing. They dunk them in filtered water tanks, then blast them with high-pressured water hoses. "But the two shrimp were either too small or buried too deep inside rock crevices," Cripe says.

Apprehending the criminals has proven tricky. Mantis shrimps move fast, burrow in rocks, and rarely make an appearance. Why not drain the exhibit? The 1,300-gallon home contains over 50 species of corals, dozens of Indo-Pacific fish, and 1,300 pounds of rock. "Not only will that be a lot of work," says Cripe, "it'll harm the delicate ecosystem."

Determined to nab the culprits, Cripe baited a special trap: one of the feisty shrimp wandered in, but quickly escaped. In a rare sighting, Cripe nabbed Sparky with a pair of tongs. Since any solution could prove more devastating to the tank's ecosystem than harboring one mantis shrimp, "I guess we just have to keep replacing the snails and crabs until we catch the bugger," Cripe sighs.

FAST FACT: There are over 500 species of mantis shrimp ranging from one-half to 16-inches long.