They are native, but they’re nasty. They seem like a creature from a horror movie, slithering out of the mud and breaking into innumerable progeny when you try to grasp them. There’s something about eyeless creatures that adds to the creepy factor.
These are milky ribbon worms, Cerebratulus lacteus, are “the other” voracious predator that threatens coastal shellfish resources. Most people have heard of green crabs and likely seen them scurrying around the rocks. Green crabs are an invasive species from Europe that have reproduced in great numbers along the Northeast coast and devoured native soft shell clam populations. They may also have opened up an opportunity for milky ribbon worms to claim new territory on the mud by reducing the clam numbers.
One of the reasons milky ribbon worms may be less in the spotlight than green crabs is that they are rarely seen by the casual observer – spending most of their time burrowed in the mud. Even the evidence they leave behind is rather inconspicuous. Rather than crunch through the shells of clams like green crabs do, they liquefy their prey from the inside and slurp them out, leaving hardly a trace. A hungry milky ribbon worm inserts its proboscis into one of the clam’s siphons, injects it with a digestive toxin that dissolves the meat, and then, sucks it back out. What’s left behind is a series of shockingly empty shells.
The other difference in their consumption of prey is their size preference. While green crabs often choose smaller clams including many below marketable size, milky ribbon worms seem to prefer clams larger than an inch across. Obviously, predation on both the young clams and those of harvestable size is problematic, but there’s something even more maddening to have a predator focus on the same clams the harvesters are after.
Ribbon worms are part of a family of worms called Nemerteans. These are flatworms that are so simple they hardly even look like they have a head. They have no eyes and only primitive sensory organs at one end and a slightly tapered tail at the other. Cerebratulus lacteus is named for its milky (lacteus) white color, although it can sometimes be pinkish. Cerebratulus doesn’t refer to the worm’s cerebrum, or brain, since it doesn’t really have one. Instead, it describes to how a coiled up worm might look like the wiggly foldings of a brain. They can grow up to four feet long and be up to an inch in diameter. They are found on both sides of the North Atlantic and like to slither into the soft mud where they can hide from predators, which ironically include green crabs along with horseshoe crabs, birds and some flounder species.
They’re not only good at hiding from predators, but they are also good at evading human attempts to control them. Because they can reproduce by fragmentation, grabbing one to toss into a bucket results in that one worm becoming two or more worms. Efforts to trap them haven’t been effective, but researchers have found that you can keep them out by covering areas with very fine screening – something that has also been done to protect from green crabs. This is obviously not feasible for large areas of clam flats, however.
There could be some positive uses for these slimy eyeless villains, however. The toxins that they use to liquefy their shellfish prey has also been shown to break down red blood cell membranes in humans. This could have some medical applications that we have yet to discover and harness. As always, once there’s a market for a species, someone will find a way to capture them in great number.
And who knows, maybe the green crabs will decide to eat them instead of the clams after all.
Copy the Story LinkComments are not available on this story.
Send questions/comments to the editors.
