Originally from the Atlantic coasts of Europe and northern Africa, the green crab has crossed the ocean to move into many coastal areas of the Americas, and has recently been found on the west coast of the United States.
This crab likes well-protected rocky shores, tidal marshes, and sand flats. It's a voracious and versatile predator that can threaten the existence of shellfish, especially mussels, when it moves into a new area.
The green crab's color actually varies from green through orange to red during its molting cycle. The abdomen has patches of yellow and there are five spines on each side.
The adult green crab ranges from 2 1/2 to 3 inches long.
Clams, mussels, oysters, and smaller crabs make up the bulk of the diet. The green crab is very quick and dexterous, and it can learn new skills for handling and opening prey as it forages.
Males generally forage at high tide, while the females do their foraging mostly at night. A green crab can open an oyster or mussel shell of up to 2 inches in length, and can consume as many as three dozen mussels a day.
Mating varies widely with the geographical area, but takes places mainly from June into October. The male mates with a newly-molted female, who then usually moves to deeper, colder water.
Eggs aren't extruded until the following spring. Larvae gather on the surface and grow in the open sea, then float ashore on flood tides as juvenile crabs, usually during August. At that time, they're less than quarter of an inch in width. They reach adult size after about two years, when they also become sexually mature.
The maximum life span for the green crab is five years.