Find out lots of information about the UK’s only native crayfish, the rare and fascinating White-clawed crayfish (White-claws). This fantastic freshwater invertebrate is very rare and its numbers are declining due to impacts from introduced crayfish species such as the North American Signal crayfish and due to the loss of suitable habitat.
What is a White-clawed crayfish
The White-clawed crayfish (Austropotamobius pallipes) is the UK’s only native crayfish species - the White-claws originate from the UK whereas other crayfish species have been introduced from other countries. Since the 1970s there has been more than a 50% decline in the areas where White-claws occur in England and Wales and they are still declining rapidly both in numbers and in the places where they are found.
The White-clawed crayfish is one of our largest freshwater invertebrates and they grow up to 12 cm long. They are omnivorous so they are not fussy eaters and eat everything from other invertebrates to carrion and water plants.
White-claws have large pincers (claws) that are coloured cream or rosy white on their underside, and it is these distinctive claws which have given White-claws their name. The carapace is generally brown to olive in colour with a pitted appearance. However, all colour variations have been observed, including blue and red White-claws. They are nocturnal creatures and aren’t very active during the winter, which means that this secretive invertebrate is rarely seen.
They have important roles in the freshwater environment because of their diet and as well as providing food for other animals such as fish, herons and otters. They are also important indicators of good water quality as they are intolerant of pollution. Find about more about the life cycle of crayfish in our downloadable poster.
Where do White-clawed crayfish live?
White-clawed crayfish are found in rivers, streams, lakes and other aquatic areas across much of England, Wales and Northern Ireland. Crayfish need water that contains minerals to build their body armour (shell) just in the same way as we need calcium to grow teeth and nails. They can also live in large ponds and canals, and even drainage ditches but they generally prefer areas with clean mineral-rich water and overhanging banks and plants.
White-claws can live up to 12 years and they usually have their first young when they are 3 years old. They are very attentive mothers with females carrying their eggs for 9 months until they hatch and even after they have hatched the young hitch-hike on their mothers for a further 2 weeks. Download our diagram of a year in the life of a White-claw crayfish.
Introduced, invasive crayfish
We have at least 6 species of introduced crayfish living in the wild in England, fewer species in Wales and Scotland and no introduced species in the wild in Northern Ireland. Most of these species were brought to provide food or angling bait and they then escaped into the wild. Many of these introduced species have a negative impact on our White-claws and our rivers. They are highly invasive and are spreading through our rivers and streams quickly, much of England and parts of Wales and Scotland have already been colonised. They often spread a disease, the crayfish plague, which kills the White-claws. The invaders also compete with White-claws for shelter, by eating large quantities of invertebrates and juvenile fish, and by burrowing into riverbanks.
There are links to two other crayfish as well. The Redclaw crayfish is the only crayfish that is allowed to be kept in aquaria (in England and Wales). It is thought to be unable to breed in our cool summers. The Marbled crayfish has been found, illegally, in the pet trade in the UK. There are concerns that Marbled crayfish might be released into the wild from aquaria and become new invaders. They could invade streams and lakes and harm White-claws and other wildlife.
Some river systems do not have any introduced crayfish. It is vitally important that they remain free from them in future too. Never move crayfish to new sites. It is a criminal offence. The only exceptions are for approved projects to help White-claws.
You can help to protect the White-clawed crayfish by texting CRAY22 £3 to 70070 to make a donation towards this project.