European green crab

The European green crab (Carcinus maenas) is a small shore crab (adults measure about 3" across) whose native distribution is along the coasts of the North and Baltic Seas. Although known by the common name of green crab, the shell (carapace) color can vary from dark, mottled green to orange or red, with yellow patches on the dorsal carapace. The crab is an able and effective forager—capable of learning and improving upon its food-gathering skills. Studies have shown that the green crab is quicker and more dexterous than most crabs, and can open bivalve shells in more ways than other crabs. One adult crab reportedly can eat 40 half-inch, clams each day and can devour crabs as large as itself. Green crabs also prey on numerous other organisms--making these crabs potential competitors for the food sources of native fish and bird species.

The green crab has already invaded numerous coastal communities outside of its native range, including South Africa, Australia, and both coasts of North America. An able colonizer and efficient predator, this small shore crab has the potential to significantly alter any ecosystem it invades. It has been blamed for the collapse of the soft-shell clam industry in Maine.