ON THE WILD SIDE
EDIBLE crab sounds delicious, but if you find one on the shore it is illegal to take it home unless it is big enough to eat. Settle for dressed crab from your local fishmonger instead.
Every one of our British crabs lives in the sea. That may sound obvious, but there are species that live in fresh water and some countries even have “land” crabs.
All have 10 legs, the front pair having evolved into powerful claws, and nearly all crabs walk sideways or backwards. They all shed their skins and grow a new softer shell or “carapace” beneath it. This stays soft for around three days after shedding. Crabs are vulnerable to predators at this time.
During their shed, lost limbs re-grow. Despite what people may have told you, research suggests that crabs can feel pain and will remember something that hurt them and stay away from it.
Crabs don’t just scuttle out of their eggs as fully formed crabs. When they hatch they are tiny larvae, a little like crab tadpoles.
They swim around the ocean eating plankton until they are big and heavy enough to sink to the bottom and begin their lives on the sandy floor.
A group of crabs is called a “cast”, but you are unlikely to find one except around a particularly smelly dead fish. Our biggest crabs are the spider crabs, with the spiny spider crab growing a carapace of up to 20cm. This doesn’t look that big compared with its relative, the Japanese spider crab. It can grow to five metres including the legs. Some species stay soft all the time, not just when shedding, like the pea-sized pea crab which lives among clusters of shellfish.
We also have 15 species of hermit crab (inset above) which take over the shells of dead shellfish such as whelks. The “shore” crab we see in rockpools has a horrible parasite. The “crab hacker” is a barnacle that attaches to its genitals, castrates it and then makes the poor thing the host for its own eggs. Ouch!