Black-fingered mud crab, top view.
Black-fingered mud crab, top view.
Irene H. Stuckey, courtesy of R.I. Natural History Survey

Black-fingered Mud Crab (Panopeus herbstii)

Alternate common name: Atlantic Mud Crab.
Color: Mud colored with stout, black-tipped claws.
Size: 3/4 inches wide and 1 1/4 inch long.
Habitat: Under stones and among masses of sponges and seaweeds, oyster beds.
Seasonal appearance: All year.

Description

Black-fingered mud crabs are small, brown colored crabs with large black-tipped claws. They are the largest species of mud crab found in Rhode Island. The tips of their pinching claws are powerful enough to crack the shells of small quahogs. The claws of the black-fingered mud crab are unequal in size. The larger claw has a large tooth, which makes this crab distinguishable from other mud crabs.

Several species of mud crabs are found in Rhode Island, differing mainly by the size and shape of their claws. Another common species of mud crab is the white-fingered mud crab (Rithopanopeus harrissi). These crabs are smaller, on average, than the black-fingered mud crab, with distinct white-tipped claws and white striped legs.

Black-fingered mud crab, underside.
Black-fingered mud crab, underside.
Irene H. Stuckey, courtesy of R.I. Natural History Survey

Life History and Behavior

Black-fingered mud crabs are generally found anywhere there is adequate protection. This includes the areas near pilings, sponges and bryozoans, oyster shells, rocks, and soft mud. They prey on young shellfish, mostly in oyster bed communities. Using their heavy, stout claw, they crush the shells of small mussels, barnacles, and American oysters.

Special Notes


Adapted from The Uncommon Guide to Common Life on Narragansett Bay. Save The Bay, 1998.