Aside from Disney’s Sebastian and Tamatoa, crabs aren’t known for their acoustic skills. The ghost crab may change that. The beach-dwelling crustacean can create loud rasping sounds, not only with its claws, but also with its guts, new research reveals.
Scientists have long known that ghost crabs (Ocypode quadrata)—native to Atlantic coast beaches of the United States—could create noise by rubbing together a series of ridges on their claws, a bit like crickets do. This “stridulation” is often a response to threats—either from a predator or another ghost crab. The noises are believed to be both a warning (like a rattlesnake’s rattle) and an indicator of a crab’s size and strength.
Now, researchers have discovered that ghost crabs can make a similar noise from elsewhere in their body. The scientists set up a series of microphones around ghost crab tanks and provoked the animals with rods, other crabs, or spiderlike remote-controlled toys. A vibration-sensing laser paired with x-ray imaging allowed the team to pinpoint a nonclaw noise coming from a small, comblike structure the crabs use to grind up food in their foregut (called the gastric mill). By rubbing the teeth of the comb across another structure called the medial tooth, the animals are able to create a sound similar to claw stridulation (listen below). The frequency (about 2 kilohertz) is audible to many of the crab’s common enemies such as birds and raccoons, as well as to other ghost crabs (and humans).
Using the gastric mill for communication frees up the ghost crab’s claws for fighting and defense and even allows the animals to communicate during battles, enabling them to broadcast their size to intimidate rivals. The researchers hypothesize that the crabs may rely on their claws to make noise when threats are farther away, but then switch to the stomach system when the danger closes in.