The Chinese mitten crab takes its name from its large, white-tipped claws, which are covered in soft fur and resemble mittens.
Chinese mitten crabs can grow to the size of dinner plates
Chinese mitten crab facts
Scientific name: Eriocheir sinensis
Family: Varunidae
Diet: A relentless omnivore, it eats aquatic plants, algae and detritus, as well as various invertebrates including worms, snails, fish (and fish eggs), shrimp and small crustaceans.
Size: 5-18cm (the length of its body alone can be as long as 6cm, whilst its legs can stretch to 12cm)
Weight: 45-160g
Lifespan: 1-5 years
Chinese mitten crabs in Britain
Originating from south east Asia, mitten crabs were first discovered in England more than 70 years ago. It's thought they were accidentally transported here and elsewhere in Europe in the ballast of ships, or by clinging onto the hulls.
Why are Chinese mitten crabs a problem?
Adults thrive in fresh or brackish (slightly salty) waters. Combine this with their favoured habitat of soft, muddy waterway banks, and it'll be no surprise that they can be found in our canals and rivers.
Their extensive burrowing leaves fragile canal and riverbanks riddled with holes and vulnerable to collapse, which in turn puts waterside structures at risk too. They have been known to block water drainage outlets, damage fishing nets with their sharp claws, and outcompete native wildlife for space.
Mitten crabs are omnivores, meaning they eat both plants and other animals. They have ravenous appetites and will take on almost anything that gets in their way, putting native species at risk of decline.
These crustaceans can be grey-green or brown in colour. They are most distinguishable by their white-tipped claws, which are covered in fine hair and resemble furry mittens. Not all juveniles develop a winter look, and instead may just have fully white claws. Mitten crabs also have long, hairy legs.
How to Chinese mitten crabs breed?
In the UK, starting in October and continuing until February, mitten crabs migrate from freshwater to saltwater to reproduce. They have been known to travel up to 1500km towards the sea in order to successfully breed. If needs be, they are even capable of crossing dry land to enter a new stretch of water.
A female lays up to one million eggs, which are attached to the underside of her abdomen. Once hatched, they become planktonic larvae, meaning they drift around in the water through a variety of developmental stages until evolving into juvenile crabs a couple of months later. As they age, these youngsters make their way back to freshwater habitats, before the cycle begins again.
Chinese mitten crabs only breed once. Both sexes die after soon after reproduction.