How spiny lobsters make scary noises

On an evolutionary tree, spiny lobsters sit near crickets. Yet musically, the crustaceans belong closer to a person torturing a violin.

Crickets make the sound track for summer by rubbing a hardened scraper, against a patch of ridges. One of the insects forewings carries the scraper and the other has the ridges. In the May 10 Nature, Sheila N. Patek of Duke University in Durham, N.C., reports that spiny lobsters rely on an entirely different mechanism to generate their raspy racket.

People grappling with spiny lobsters above and under water have gotten an earful of the creatures harsh rasping sounds. Its very abrasive, Patek says.

Rather than being hard like most of the animals carapace, a lobsters scraper or plectrum–a pink protrusion at the base of each antenna–has a more leather like texture.

Observers have seen spiny lobsters scrape their leathery plectra across scaly ridges below their eyes. At first, Patek assumed that even this soft scraper could rasp the way crickets do with their harder one.

After using underwater microphones and high-speed videos to catch the Caribbean spiny lobster (Panulirus argus) in the act of making noise, Patek recalls saying to herself, Wait a minute! Thats not whats going on.

She could see that a lobster plectrum moves jerkily and that sound comes only when the plectrum slides, not when it sticks. If the lobsters were depending on a cricketlike washboard mechanism, the sound would coincide with the plectrums impact with a ridge peak.

Patek concludes that the lobsters make their noises by drawing their plectra in a stick-slip movement across the ridges. Its much like a violin bow pulling across a string, she says. This stick-slip mechanism is also behind the tooth-tingling sounds of a finger squeaking over the surface of a balloon, she explains. The process enables a lobster to scratch out alarms and protests even at molting time, when its body is soft and most vulnerable.

The clawed lobsters of culinary import make noise, too, Patek points out, but they rely on a swiftly vibrating muscle in their heads.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.