Can a parasitic worm help rebuild the Bay’s blue crab population?

Parasitic worms might sound like bad news for blue crabs—but they could actually be a powerful tool in saving them. A new study out of William & Mary’s Batten School and the Virginia Institute of Marine Science (VIMS) reveals that a tiny egg-eating worm could help revive the struggling Chesapeake Bay blue crab population.

The worm, Carcinonemertes carcinophila, lives on the eggs of female crabs. While it doesn’t cause major reproductive harm, researchers found that its presence—and color changes after feeding—can indicate whether a crab has spawned. That’s critical information for fishery managers trying to reverse record-low crab numbers, as found in the latest Winter Dredge Survey.

One big question was whether the worm could survive the Bay’s low-salinity tributaries. Lead author Alex Pomroy, working with Ph.D. student Alex Schneider and Professor Jeffrey Shields, found that not only do the worms thrive in saltier waters, they can also survive lower salinity levels once thought to be lethal.

This opens the door to using the worms as biomarkers throughout a crab’s life. And that matters—because first-time spawners, or “primiparous” crabs, produce far more offspring than those that have spawned before.

By identifying which crabs are the most reproductively valuable, scientists and regulators can target protections more effectively.

This tiny worm may just hold the key to rebuilding the Bay’s iconic blue crab fishery.

For the Chesapeake Bay’s future, it turns out the answer might be hiding in plain sight—on the backs of its blue crabs.