Common shore crab

The common shore crab is a tough little crab found along rocky coasts and in rock pools. It has a wide, flat shell, ten legs, and two front legs tipped with pincers. Most shore crabs are green, which helps them hide among the seaweed and stones. When the tide slips out, you can often spot one scuttling quickly for cover under a rock.

Watch a shore crab move and you will see it hurry sideways rather than forwards. Its legs are built for a speedy side-shuffle across slippery rocks. The two pincers at the front are handy tools. The crab uses them to pick up food, to nip off tasty bits, and to hold on tight when it wants to stay safe and tucked out of sight.

Shore crabs come in many colours. Youngsters wear mottled patterns of green, grey and cream, like tiny pebbles. As they grow older, some turn orange or even red underneath. These changing colours help a crab blend into its home, whether that is dark seaweed, pale sand, or a shell-covered seabed. A well-hidden crab is a safe and happy crab.

A shore crab will eat almost anything it can find. It is an omnivore, munching mussels, snails, worms, seaweed and even scraps that other animals have left behind. This makes it a helpful tidy-upper of the shore, clearing away leftovers. It hunts and scavenges mostly around the water's edge, poking into cracks and peeking under stones for its next meal.

This crab is native to the coasts of Europe and North Africa. It has also been carried to other parts of the world by ships and other human travel, and in those new places it can become a serious invasive species that scientists monitor closely. Like all crabs, a shore crab wears its skeleton on the outside, so to grow bigger it must slip out of its old shell and grow a roomier one, a little at a time.