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Deep-sea worms feast on the teeth of dead sharks that fall to the seafloor. These worms were previously known to eat whale bones and the remains of bony fish, but when those are scarce, shark teeth may be a key source of food.

Osedax worms are strange-looking creatures with frilly pink gills. They have no mouth or stomach, so they rely on microbes living inside them to absorb collagen from bones. These so-called 鈥渮ombie worms鈥澛爓ere first discovered in 2002 on whale falls, the bodies of dead whales that have sunk to the sea floor.

Until now, they were thought to feed exclusively on the collagen and lipid components of bone 鈥� fittingly, their Latin name means 鈥渂one eater鈥�. Traces of these worms have been discovered in fossils dating to the Cretaceous Period, suggesting that they predate the whales that they are best known for feeding upon.

鈥淚t seemed a logical step to see if they could have been attacking another source of collagen,鈥� says at the University of California, San Diego. 鈥淲e knew the cartilage is rich in collagen and that sharks had been around longer than bony fish.鈥�

Hoping to see whether Osedax were able to exploit the remains of cartilaginous fish as well, he and at Occidental College in California sunk mesh bags containing the jaws of three common thresher sharks (Alopias vulpinus) in Monterey Bay, California, in 2018. The jaws fell to a depth of about 1000 metres in the Monterey Submarine Canyon.

The researchers returned eight months later and drew the bags back up to the surface. There were few remaining traces of the jaws themselves, but of the 40 remaining teeth, 10 had been colonised by two species of Osedax worms.

The worms had all inserted themselves through the softer roots of the teeth, indicating that they were after the collagen-rich dentine within. These zombie worms secrete an acid to penetrate bone, but they were unable to dissolve the enamel on the crowns, which is harder than the bone that they typically feed on.

The finding suggests that shark carcasses 鈥渕ay be one of the stepping stones that keep the population going between whale falls鈥�, says at the National Museum of Natural History in Washington DC.