The animal on the cover of Ruby Best Practices is a green crab (Carcinus maenas). Also
known as a European shore crab, it is native to the coasts of the North and Baltic Seas.
Although relatively small—adults measure three inches across—an adult green crab
can consume up to 40 clams each day and can eat other crabs as large as itself. A
voracious predator, the green crab also preys on oysters, mussels, and snails,
competing for food with many fish and bird species.
Despite its name, the green crab’s shell color can vary from dark green to orange or red,
sometimes with yellow patches on its underside. The abdomen of the male is triangular
in shape, whereas the female’s is broader and rounder. Males and females also react
differently upon being picked up: males typically stretch out their legs, whereas females
fold them in, a behavior known as the egg-protection reflex.
A natural colonizer, the green crab is potentially destructive to any ecosystem it invades.
It has already invaded many coastal communities outside of its native range, including
Australia, South Africa, and North America, where it is blamed for the collapse of the
softshell clam industry in Maine. It is ranked number 18 on the list of the 100 world’s
worst invasive types of species. Numerous efforts around the world have been made to
control invading populations, to varying degrees of success. One of the more effective
experiments has been on Martha’s Vineyard, Massachusetts, where the town of
Edgartown pays bounty hunters 40 cents per pound of green crab; more than 10 tons
have been caught and destroyed as a result.