Osedax, also known as zombie worms or boneworms are tiny worms (1 to 3 inch long) found deep below the ocean's surface. The name “zombie worms” alludes to the worms’ behavior of boring into the bony remains of whales to reach the fatty lipids. They were first discovered while feeding on the carcass of a grey whale in 2002 by a team of researchers studying the depths of Monterey Bay, California. Since then, more than 15 species of the worm have been discovered in the oceans. Boneworms do not feed on minerals on the bones but seek out and digest the fat deposits. They do not have a mouth, teeth, or stomach but instead feed by secreting an acid that dissolves bones to expose fats that are digested by symbiotic bacteria. Researchers are yet to understand how the boneworms extract nutrients from the bacteria, but hypothetical studies suggest that they digest the bacteria.
Behavior Of Zombie Worms
While the worms are known for extracting nutrients from the remains of whales at the seafloor, they do not discriminate among bones. They have also been observed on the bones of other fish, and other bones dumped by ships. Osedax remains attached by drilling and inserting their heads into the bones. The feathery plumes at the other end of the body act as gills that extract oxygen from the water. Only the female worms do the drilling, the microscopic males live within the female’s body and derive nutrition from the female. One study counted more than 100 male worms inside a female’s body. This unique feature eliminates the need to search for a mate since the sperm and the eggs are close together. Once the eggs are fertilized, the boneworm spreads them far and wide to increase their chances of surviving.
The exact role of Osedax remains controversial with some researchers claiming that the worms are specialists on whalebones and feed on the other bones unintentionally while others argue that they are general feeders and actively seek out other varieties of bones. The controversy arises from a biogeographic paradox: despite whale remains being rare, the worms are surprisingly diverse and inhabit a broad biogeographic niche. One hypothesis suggests that the worms can feed on the bones of other vertebrates besides whalebones. Osedax has been observed feeding on the remains of other fish and bones dropped into the ocean by vessels. Controlled experiments have also proven that the worms can feed on cow bones. However, critics argue that Osedax in their natural environment only feed on the remains of other fish when dead whales are unavailable. They further argue that a controlled environment is not the natural habitat of the boneworms, and they feed on the cow bone as a survival strategy rather than a preference.