Monster Week—Ugh! What Is That in the Fish Tank?
Another animal in the Monster Week series…
September 10, 2015
In the dark of night, the monster’s head peeks out from the surface, exposing a tiny fraction of its long, snakelike body. Five antennae detect tiny disturbances from its prey. Its sharp jaws are open incredibly wide, ready to slam shut like scissors. When its prey approaches, the creature lunges with lightning speed. If it doesn’t succeed in slicing its prey in half, the beast drags its pitiful victim into its underground lair, where it injects it with toxins (poisons) and digestive acids. Although this sounds like a scene out of a science fiction horror movie, it is actually a description of the hunting practices of the bobbit worm, found in oceans across the world.
The segmented bobbit worm belongs to the genus Eunice. Its body is made up of dozens of ringlike segments. Each segment has two pairs of stumpy leglike appendages that the worm uses to move through the sand where it makes its home. The bobbit worm is one of the largest worms, growing over 12 feet (3 meters) long. There are some reports of individuals reaching over twice that length, however. Some bobbit worms have a bright, iridescent shine.
The worm lives at the bottom of shallow, tropical oceans throughout the world, for example in coral reefs. It buries itself in sand and mud and puts out mucus (a slimy substance, such as snot) from its body to form underground tubes. From these tubes, it hunts as an ambush predator, sticking its head out of the sand and lunging at animals that stray too near. Though well known for this hunting behavior, bobbit worms are actually omnivores, eating just about anything that drifts near their lairs.
Occasionally, bobbit worms find their way into public and private aquariums, where they terrorize their tankmates and anger aquarium keepers. It is thought that young worms are accidentally brought into tanks along with sand and rock harvested from warm ocean waters. In aquariums, small worms go unnoticed, scavenging or feeding on invertebrates (animals without backbones). Eventually, however, bobbit worms grow large enough to attack fish. They typically destroy traps designed to capture marine worms. Often, aquarium keepers have to take apart their entire tank setup in order to capture them.
The bobbit worm is not very well studied. The genus Eunice contains hundreds of species, and there are likely many more to be discovered. Many parts of the worm’s life cycle and habits remain a mystery. Who can blame scientists for not studying such a scary creature?