The European green crab is native to the Atlantic coast of Europe and northern Africa. In the 1800’s the European green crab entered the Cape cod region through sailing ships. In the 1950’s they helped towards the decline of Maine’s soft shell clam fisheries. They were transported to the west coast in 1989, possibly through ballast water of ships, kelp in lobsters packaging or with Atlantic bait worms.

At this point they can be found on the shores of South Africa, Australia and both coasts of North America as well as their native range.

These crabs can have a dramatic impact on smaller shore crab, clams, and small oysters which it eats. It is also more efficient in feeding than many native crabs and competes for food with native fish and birds as well.

It can be confused with helmet crabs or hairy shore crab but has five spines or teeth on each side of the shell near the eyes. The crab is not always green, but may be mottled green or brown and sometimes orange and red. Adults range from 2.5 inches to 4 inches. It has a high tolerance for wide ranges of temperature and water salinity. They can produce 200,000 eggs in one reproductive cycle and have been know, rarely, survive up to two months out of water.

Means of controlling the threat they pose has been to educate boaters, increase regulation, inspecting arriving boats and setting up volunteer programs with citizens, crab fisherman and oyster growers to catch the crabs in wire mesh traps baited with fish. On the east coast bounties have been placed on the European green crab to reduce their numbers.

(From: http://wdfw.wa.gov/fish/ans/identify/html/index.php?species=carcinus_maenas and http://www.columbia.edu/itc/cerc/danoff-burg/invasion_bio/inv_spp_summ/Carcinus_maenas.htm)