Crustacean Cacophony

by David Sugarman

Spiny lobsters can make a loud rasping sound when they are threatened by predators. This probably startles the predator, either scaring it off or giving the lobster time to get away.

Spiny lobsters make these sounds by rubbing a plectrum—like the pick used to pluck a guitar—at the base of their antennae against a file just below each eye. It's different from the way crickets make their chirps, because the plectrum in the lobsters isn't hard tissue.

So how is such a loud sound produced from rubbing soft parts together?

A scientist in the U.S. devised a way to detect the motion of the plectrum and measure the resulting sound. Using an underwater microphone and attaching a motion detector to the plectrum, she found that a very high-frequency sound was produced—one much higher than what would result from the plectrum just rubbing over the file's microscopic ridges.

The abrasive sound appears to be made by the plectrum repeatedly sticking then slipping as it rubs over the file. This is what happens when a bow is drawn over the strings of a violin. But it's the first evidence of this type of mechanism in nature.

Lobsters are usually protected by hard shells. But to grow, a lobster must shed its shell, and is vulnerable to attack until the new one hardens. So the ability to deter predators with sounds made by rubbing soft tissues together is a handy talent for a spiny lobster to have. Even if it's not exactly a pelagic Perlman!