The first animal known to use internal teeth as a vocal cord

Science · Published 8 October 2026 Swipe more like this →

In short: Most crustaceans have internal teeth for grinding food, but ghost crabs have evolved a much more sophisticated use for them. When threatened, these crabs produce audible growls by vibrating their stomachs—a unique form of acoustic communication that allows them to warn off predators without moving a muscle.

When Jennifer Taylor and her colleagues at the Scripps Institution of Oceanography observed ghost crabs (Ocypode quadrata), they noticed a strange behavior. Even when the crabs held their claws in a fixed upright position—preventing the usual rasping sound made by rubbing joint ridges—they still produced a distinct, audible growl when approached by threats like toy crabs or small robots. The researchers observed these sounds were loud enough for humans to hear without any equipment. This behavior occurs specifically when another animal gets too close.

To solve this mystery, researchers took the crabs to a hospital X-ray department. Using X-ray fluoroscopy, they were able to see inside the animals' bodies in real-time. The footage revealed that the rasping sounds coincided exactly with the movement of teeth in their foreguts, known as gastric mills. Crucially, the crabs were not actually grinding food during these episodes; they were deliberately vibrating the teeth against one another. The study involved a specific species called Ocypode quadrata. These internal structures are technically referred to as gastric mills.

While many animals possess gizzards or stomachs capable of making noise—such as birds swallowing stones or certain worms and molluscs—the ghost crab is the first crustacean identified as using internal teeth specifically for communication. This mechanism is remarkably similar to that of some fish, like grunts, which produce sounds using teeth in their throats. Dinosaurs also possessed internal teeth for grinding food, though they did not swallow stones like modern birds do. This makes the crab's behavior quite distinct among various taxa.

This discovery highlights a fascinating evolutionary leap in animal behavior. It suggests that complex communication doesn't always require specialized vocal cords or external limbs; sometimes, the most effective way to project a warning is from the inside out. This discovery provides a new perspective on how marine life interacts with its environment. It proves that acoustic signals can be generated through internal mechanical friction.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• Pacific mole crabs use specialized physics to burrow into wet sand at lightning speed
• The Terrible Crabs of the Cambrian: Meet the Ocean's First Apex Predators
• True crabs hid their tails and conquered the seafloor
• The ghost shrimp is not a shrimp, but a master of ocean floor architecture.
• Ghost crabs are masters of the beach, but they can actually drown in the ocean.
• How three intrepid women redefined our relationship with the primate world
• Why genetic diversity is the ultimate insurance policy for every living species on Earth
• The mathematical blueprint for genetic stability in a population
• When isolated populations collide, they create a genetic engine for rapid evolutionary change
• The mathematical ideal of a population that never changes
• Evolution is not just a tree; it is an intertwined net of genetic exchange.
• Why do some genetic traits persist in populations instead of vanishing over time?

More in Evolutionary biology · More in Science · Latest · A–Z · All topics