How Bone-Eating Zombie Worms Drill Through Whale Skeletons

The worms use a “bone-melting acid” that frees up the nutrients within both whale and fish bones

A bone-munching worm eating a fish bone.
A bone-munching worm eating a fish bone. Scripps Institution of Oceanography

In nature, nothing goes to waste. The relatively recently discovered so-called “bone-eating zombie sea worms” feast their way through thick whale bones and reduce the final remains of the once massive animals into dust. The BBC reported last year on what we knew about this mysterious, slightly terrifying genus of creature, called Osedax:

The unusual group’s name Osedax is Latin for “bone devourer”, and the worms have no mouth, gut or anus yet are still able to remove nutrients from bones.

Previous studies have revealed that symbiotic bacteria inside the worms digest the fats and oils extracted, but the question of how the worms physically bore into the bones had been a mystery.

Close analysis of the worms failed to find any abrasive structures the worms could use to mechanically “drill” into bone.

As it turns out, however, these worms don’t just eat whale bones. They eat fish bones, too. Researchers from the University of California, San Diego, are narrowing in on just how the tiny worms pull off their bone-disintegrating feats on these various deceased species.

To conduct their study, the team used remotely operated vehicles to deposit tuna, wahoo and shark remains inside cages off the coast of California. Five months later, they retrieved the remains and found the worms living inside. The shark cartilage, however, had already been picked apart by other mystery animals.

The worms use what the researchers call a “bone-melting acid” that frees up the nutrients within whale and fish bones. The acid releases and absorbs collagen and lipids within the bones. The researchers continue:

Because they lack mouths, bone worms must use an alternative method of consuming nutrients from whale bones. Bacteria that live symbiotically within the worms are involved in this process, however, the exact mechanism is not yet fully understood. Some evidence suggests that the symbiotic bacteria metabolize bone-derived collagen into other diverse organic compounds, and that the worms subsequently digest the bacteria for their own nutrition.

The worms mostly turn up in whale bones, but this study confirms that they sometimes occur in fish bones, too. This finding makes researchers suspect that the genus might have evolved millions of years ago, before marine mammals existed. So far, 17 species of the strange worms have been found in oceans around the world.

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