Ghost crabs growl using the teeth in their stomachs to ward off predators

The peculiar behaviour is believed to be the first evidence of an animal using its stomach to communicate.
By Australian Geographic September 11, 2019 Reading Time: < 1

LIKE MOST CRABS, ghost crabs use their strong claws to fight off predators, but they have an additional defensive technique in their arsenal: they can further intimidate by growling… using the teeth in their stomachs.

Named for their sand-coloured carapaces, which allow them to move about inconspicuously, as well as their nocturnal habits, the ghost crab can be found along most Australian shorelines. 

This new discovery about the crab, published today in the Royal Society B journal, is the first evidence of an animal using its stomach to communicate.

The researchers from the University of California stimulated these raspy reactions by taunting the crabs with dead and live ghost crabs, a plastic toy crab and a remote control robotic toy.

It’s normal to hear ghost crabs making noises called ‘stridulations’ by rubbing their pincers together, but lead author Jennifer Taylor could hear something else coming from the inside.

A gastric mill within the ghost crabs’ stomach, made up of teeth, is typically used to grind up their food, but x-rays found they also use the teeth to produce a sound akin to that of a growling canine.

The research paper says that the crab’s claws are effective for deterring predators from far away, but that growling may be more useful for close-up interactions as they can continue to convey “size and aggression information acoustically while their weapons are in use.”

The findings, the researchers believe, reflects an important moment in ghost crab evolution where their defence and social skills advanced.