Growling Ghosts and Beatboxing Behemoths! The Surprising Percussive Prowess of Crabs

In a list of noisy animals, crabs wouldn’t crack the top 20—maybe even the top 50. Lions? Check. Wolves? Sure. Parrots? Gotcha. Howler monkeys? Of course. 

But crabs? We usually think of them as the strong silent type. Since they lack a voice box, they can’t roar, squawk, or make many of the other sounds that mammals and birds can. Vocalizing crabs are only found in cartoons—usually singing to mermaids about the wonders of living under the sea.

In the real world, crabs can’t match the crooning capabilities of Disney’s Sebastian, but their surprising percussive prowess could land them a spot in his “hot crustacean band.”

Growling Ghosts

Unsuspecting beach goers in the eastern United States shouldn’t be startled by guttural growls emanating from the sand. These are just the moans of angry ghosts—ghost crabs that is. 

Atlantic ghost crabs (Ocypode quadrata) get their moniker from their pale-colored bodies, eerie club-shaped eye stalks, and nocturnal lifestyles. The crabs burrow beneath the sand during the day, emerging after sunset to forage for insects, clams, small crustaceans, and sea turtle eggs.

These fleet-footed crustaceans can travel more than 300 feet (91 meters) on their evening excursions, but they don’t always make it back to their burrows before sunrise. Digging a new home takes time and energy, so stranded crabs often attempt to commandeer other crabs’ burrows, regardless of whether they are already occupied. This leads to ongoing conflicts between trespassers and tenants—with combatant crabs lunging, snapping, and growling to showcase their size and strength.

Ghost crabs usually generate growls (or rasps) by rubbing specialized ridges on their claw against another structure at the base of their limb. This process, called stridulation, is common among crustaceans and similar to the way male crickets produce their signature chirps.

But stridulation requires ghost crabs to fold their claws toward their bodies and prevents them from snapping their pincers, a definite disadvantage during skirmishes. So, the crabs developed another way to voice their displeasure.

Using their gastric mill, a structure in the stomach that normally helps them grind up food, the crabs produce guttural growls. Muscle contractions cause comb-like plates to rub along a hard medial tooth, similar to percussion instruments like guiros or washboards. 

Crabs can modulate the duration and frequency of their growls by changing the grinding stroke of the combs against the tooth. Larger crabs produce lower-pitched noises—much like bass drums make deeper sounds than smaller snares.

Beatboxing Behemoths

Like their rasping relatives, coconut crabs (Birgus latro) know how to sound off. Using their mouthparts instead of their guts, these colossal crabs can play a variety of ditties—but they seem to have a soft spot for love songs. 

Coconut crabs are the largest terrestrial crustacean, reaching up to 39 inches (1 meter) across and weighing up to 9 pounds (4 kilograms). Adult crabs are land dwellers, having traded their gills for a set of branchiostegal lungs that allow them to breathe air. Because of this, they are unable to swim and will drown if submerged in water. 

With the strongest claws of any crustaceans and a bite force approaching that of adult lions, they have few predators other than humans. These omnivores feed on fruits, nuts, seeds, tortoise hatchlings, red crabs, rats, and carcasses. Adept at climbing trees, they can also snag unsuspecting seabirds from their roosts.

Because they have a well-developed olfactory system, scientists assumed coconut crabs primarily communicated through chemical cues. But evidence suggests the crabs possess a diverse acoustic repertoire.

By vibrating leaf-like appendages called scaphognathites against the hard plates surrounding their gills, they produce a variety of clicks and taps—not unlike a xylophone or timbale drum. By changing the vibration speed of the scaphognathites, they can vary the pitch and intervals of the sounds.

Coconut crabs are particularly percussive when breeding, changing the frequencies and intervals of their clicks and taps during each phase of the mating process.

Clicking and growling may not sound like music to our ears, but these noises strike a chord with crabs. Whether they’re defending their territories or wooing their dates, crabs’ lives are seldom silent. These crustaceans may lack the vocal chops of their cartoon counterparts, but their percussion skills can’t be beat.  

To read about some other unusual aquatic creatures, check out this article.