Green Crabs

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The Green crab (Carcinus maenas) is known by different names around the world. In the British Isles, it is generally referred to simply as the Shore crab. In North America and South Africa, it bears the name Green crab or European green crab.

In Australia and New Zealand, it is referred to as either the European green crab or European shore crab.

Green Crab Characteristics

Green crabs are dark green in color with yellow or brown blotches. Mature female Green crabs are orange-red underneath. Their shell, or carapace, is about 3 inches (8 centimetres) wide and relatively square-shaped. Green crabs have five points, or spines, along the carapace.

Green crabs which delay molting become red–colored rather than green. Red individuals are stronger and more aggressive, however, they are less tolerant of environmental stresses, such as low salinity (salt content of a body of water) or hypoxia (a phenomenon that occurs in aquatic environments).

These swimming crabs are omnivores, being both predators and scavengers, consuming the widest array of marine animals and plants known for any crab in the world.

Originally from Europe, Green crabs arrived in Narragansett Bay approximately 200 years ago and are found on rocky shores, mud flats, salt marshes and tidal pools. By 2001, however, the Green crab was far more common in the subtidal zone in southern New England than in the intertidal zone, the latter now occupied by the Asian shore crab.

Green Crab Habitats

Green crabs can live in all types of protected and semi-protected marine and estuarine habitats, including habitats with mud, sand, or rock substrates, submerged aquatic vegetation and emergent marsh, although soft bottoms are preferred.

Green Crab Reproduction

Female Green crabs can produce up to 185,000 eggs and larvae develop offshore in several stages before their final molt to juvenile crabs.

Young crabs live in ‘Posidonia oceanica’ meadows (the botanical name of a genus of flowering plants) until they reach adulthood.

Physical Features and Moulting

The carapace of the Green Crab is a particularly useful identifier in the field. The five teeth or spines along the front edge of the shell on each side of the eyes are a defining characteristic of the species, and the overall shape of the shell is noticeably broader than it is long, giving the crab a somewhat flattened, fan-like profile. The claws are unequal in size and are used both for capturing prey and for defence against predators and rival crabs.

Moulting is a critical and recurring process in the life of a Green Crab. As with all crustaceans, growth can only occur when the old shell is shed and a new, larger one formed in its place. During this brief period the crab is soft bodied and highly vulnerable, and individuals typically retreat to sheltered spots beneath rocks or within dense vegetation until the new shell hardens. The colour change that occurs in crabs that delay moulting, shifting from the typical green to a deeper red, is an interesting biological phenomenon that also correlates with behavioural and physiological differences between the two colour forms.

Diet and Feeding Behaviour

The Green Crab’s reputation as a voracious and opportunistic feeder is well earned. It will consume almost anything it can catch or scavenge, including mussels, clams, small fish, marine worms, algae and organic debris. The claws are strong enough to open bivalve shells, making the species a significant predator of commercially important shellfish such as soft-shell clams and oysters. This feeding behaviour has brought the Green Crab into direct conflict with shellfish fisheries in many of the regions where it has been introduced.

On native European shores, the Green Crab exists within a balanced ecosystem where its numbers are kept in check by natural predators and competitors. In regions where it has been introduced, however, the absence of these controls has allowed populations to grow unchecked, amplifying the impact of its feeding on local species.

Green Crabs as an Invasive Species

Few marine invertebrates have demonstrated the same capacity for successful invasion as the Green Crab. From its origins on the Atlantic coasts of Europe and North Africa, it has established itself on the eastern and western seaboards of North America, in southern Australia, South Africa, and parts of South America. Each new introduction has followed a similar pattern, with the species rapidly colonising available habitat and outcompeting native crabs and other invertebrates for food and space.

The Green Crab’s tolerance for a wide range of temperatures and salinities makes it exceptionally well suited to surviving in new environments, and its reproductive capacity ensures that populations can grow quickly once established. Researchers and coastal managers in affected regions have been working to better understand and limit the spread of the species, with some communities trialling commercial harvesting as a means of reducing local populations while also generating economic value from the catch. Despite these efforts, the Green Crab remains one of the most successful and challenging marine invasive species in the world.

Sources & References

• Animal Diversity Web — Carcinus maenas
• Wikipedia — Carcinus maenas

Joanne Spencer (2026, April 8). Green Crabs. Animal Corner. Retrieved 2026, April 16, from https://animalcorner.org/animals/green-crabs/

Joanne Spencer. "Green Crabs." Animal Corner, 2026, April 8, https://animalcorner.org/animals/green-crabs/.