We found what someone said was a spider crab at Cape Lookout. It has legs like a snow crab. Are spider crabs and snow crabs the same thing?

September 2007

When undecorated, short, pointy knobs are visible on a spider crab’s hard outer shell.

When undecorated, short, pointy knobs are visible on a spider crab’s hard outer shell.

Same family, wrong member. The popular snow crabs served at restaurants are in the spider crab family, but they’re not the same spider crab as in our waters.

The term “snow crab” (Chionoecetes opilio) is a market name used for four species of crabs. Our lanky crabs are the common spider crabs, Libinia emarginata, and its almost identical relative, Libinia dubia. Whereas snow crabs can measure 2 feet in length and weigh 5 pounds, our round-bodied spider crabs grow to only about 4 inches wide. Their long legs, however, can measure more than 6 inches in length.

Common spider crabs such as ours range from Nova Scotia to Brazil. They can be found from the low-tide line to depths of more than 400 feet, where they move slowly across the sea floor scavenging for food. Their pincers are weak and basically useless against predators. Male crab legs and pincers are almost twice as long as those of females.

Although spider crabs can burrow into soft bottoms to evade predators, they rely primarily on camouflage. Combined with a nondescript, grayish-yellow to brown body, they can be easily mistaken for a rock or part of the sea floor. They also often decorate themselves to look like anything but a meal, adding algae and other debris to the top of their hard shell.

Interestingly, these harmless, slow-moving crustaceans belong to a group of animals currently thought to be among the first to have evolved the crab form. If you look closely at the face of a spider crab, it looks old – very, very old.