Maryland’s crabs are gluttonous cannibals, decades-long research finds

Crabs are cannibalizing each other with shocking rapacity in components of the Chesapeake Bay

By Jackie Flynn Mogensen edited by Claire Cameron

The Chesapeake Bay’s crabs are tearing themselves aside. A decades-long research of the blue crabs residing alongside the Maryland coast means that cannibalism is so rife that the crabs are their very own main predatory power.

Cannibalism is frequent among the many animal kingdom—it’s been witnessed in a range of creatures, from caterpillars and praying mantises to massive salamanders and octopuses—however how, the place and when it arises is much less understood.

In this research, researchers noticed 2,687 juvenile crabs between 1989 and 2025. The workforce tethered the crustaceans to posts at various instances of the 12 months and at various depths of Maryland’s Rhode River, a tidal estuary in Chesapeake Bay. After about 24 hours, the researchers would search for indicators of predation—mainly, if the crabs had been useless or injured. Incredibly, they discovered {that a} whopping 97 % of crab killings or accidents might be attributed to cannibalism—fish, in the meantime, had been nowhere to be discovered.

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The proven fact that the crabs had been preying on each other wasn’t a shock, says Anson “Tuck” Hines, emeritus director of the Smithsonian Environmental Research Center and lead creator of the research. “What was surprising was that we found here no fish predation—not a single instance of fish predation,” he says.

“All the predation was due to cannibalism by other crabs,” he says.

The manner Hines and his workforce labored out what had killed or maimed the launched crabs was by on the lookout for clues of their stays. If the crabs had been killed by fish, different analysis recommended there can be no crab stays left on the top of the tether line. Instead there’d be a fish—”sort of like fishing with live bait,” Hines explains. But if the crabs were attacked by their own kind and those crustaceans’ shell-crushing pincers, you’d expect to find bits of “carapace”—crab shell—or an injured crab at the end of the line.

By the end of the study period, a little more than 40 percent of all the young crabs tethered in the river showed any sign of predation. Of those, about 56 were killed “with remains” left on the line, the authors found, and about 41 percent were left “alive and injured”—both smoking guns for a cannibalistic crab culprit. In just 3 percent of predation cases, the crab went completely missing—but without a fish at the end of the line, the researchers couldn’t directly attribute these disappearances to any specific cause. (Still, even in those cases, the predators were presumed to be adult crabs.)

Hines’s research suggests that estuaries such as the Rhode River may provide an “important refuge” for the bay’s young blue crabs, which try to survive by burrowing themselves into the sediment. Fish tend to be visual predators, he says, whereas blue crabs use “chemical and tactile cues”—they dig around in the sediment to hunt, which might, in some areas, make them better at uncovering a hidden young crab.

The results could help fisheries better assess the blue crab stock in the Chesapeake Bay, information which matters for another well-known crab predator: us. Indeed, an estimated 50 percent of all blue crabs harvested in the United States for consumption comes from the Chesapeake Bay.

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