It's concert time for the Animal Philharmonic. The crickets are warming up back in percussion, flexing their wings and chirping as the elephants stomp their feet and the beavers slap their tails in warning. Over in the wind section, the songbirds are twittering nervously and pecking at each other's music. The rhinos can't actually play their horns, so there's no brass section, but otherwise the turnout is pretty good for a weeknight. All kinds of sounds, all kinds of ways to make them...and there in front, tuning their violins, are the lobsters.

Lobsters? Violins?

Yes, says Sheila Patek, a Duke University graduate student who recently discovered that spiny lobsters make sound using the biological equivalent of a violin - the first time such a mechanism has been found in nature.

"Lots of people have tried to explain how these lobsters make sounds, and most of them were wrong," said Patek, whose research appeared in the May 10 issue of Nature. "We've never seen this before."

Using an underwater microphone and tiny sensors attached to the lobster's antennal muscles, Patek showed that when a lobster moves its antennae in a certain way, a nubbin of tissue called a plectrum rubs over a file near its eyes. The rubbing motion creates frictional pulses of sound. Unlike crickets and other animals that produce sound by scraping a hard "pick" over a ridged "file," a lobster's plectrum is made of soft tissue, and the file's surface is macroscopically smooth. A lobster's sound is hardly musical - it sounds like a finger being dragged across a wet, squeaky washboard - but the underlying mechanism is similar to a violinist drawing a bow across the strings of her instrument.

Since lobsters cannot hear except at very close range, the sounds they make are probably not used to communicate with each other. Instead, the sounds serve as a defense against predators, which may be startled long enough for the lobster to escape, Patek said.

"If you were reaching down to pick up a sandwich, and it squeaked, you might pause," Patek explained.

Sound-based defense mechanisms are relatively common in nature, Patek said, "but the lobster's is unusual from an evolutionary as well as a structural standpoint. Not all lobsters are noisy, only certain species in the Palinuridae, or spiny lobster, family. These lobsters bear little resemblance to the docile creatures found in supermarket tanks. Aside from their mottled coloring, their most striking characteristic is a pair of long, stiff, spine-encrusted antennae. Several faded scratches on Patek's arms bear witness to the antennae's effectiveness as defensive tools.

During the molting period, however, the spiny lobsters' antennae and shell are too soft to protect them against predators. Instead, the lobsters must rely on scare tactics - sound - to drive predators like sharks, grouper, and triggerfish away. A sound-producing mechanism that relied upon hard surfaces would be of little use during this vulnerable stage. This suggests that the lobsters' soft-tissue-based sound structures are an evolutionary response to predation, Patek said.