We have at least 6 species of introduced crayfish living in the wild in England, fewer in Wales and Scotland but none in Northern Ireland. Most of these species were brought to provide food or angling bait but then escaped into the wild. Some are extremely harmful to our only UK species, the White-clawed crayfish, and our rivers.
Signal Crayfish (Pacifastacus leniusculus) Originally from North America, they were introduced to Sweden and Finland in 1960s and then move throughout Europe. The most abundant of the introduced crayfish in the UK and now occur in many rivers and spread along rivers, streams and canals. Signal crayfish carry crayfish plague and compete with the White-clawed crayfish for shelter. They have a ferocious appetite and a considerable impact on other freshwater animals as well as damaging our river banks through burrowing.
Narrow-clawed crayfish (Astacus leptodactylus) these crayfish are found at sites scattered throughout the midlands and south-east England including London after being originally introduced to the fish market in the 1970s. They originate from Eastern Europe and do not occur naturally in the UK. Narrow-clawed crayfish have the potential to outcompete the White-claws and can cause angling nuisance but like White-claws they are susceptible to crayfish plague and pollution.
Spiny-cheek crayfish (Orconectes limosus) Originating from Eastern USA these were introduced into Germany in 1890 and are found in south-east England and the Midlands. Spiny-cheek crayfish can carry the crayfish plague and have a considerable impact on other freshwater animals. Like Signal crayfish they burrow into river banks causing damage and they can also tolerate slightly polluted waters. Once they are abundant in a river they can spread quickly.
Noble crayfish (Astacus astacus) Noble crayfish originate in Europe but do not occur naturally in the UK. They were introduced to England in the 1980s when they escaped from a fish farm. They are only found in a few sites in Gloucestershire and Somerset. Noble crayfish are susceptible to crayfish plague, are declining in Europe and are not known to have any negative effect on White-claws.
Virile crayfish (Orconectes virilis) recorded in some lengths of river in the London area, these are the only known populations in the UK. They are not a European species and originate from the USA and Canada. Virile crayfish are likely to be carriers of crayfish plague and can increase in numbers quickly. Their burrowing activity causes damage to river banks.
Red swamp crayfish (Procambarus clarkii) these have been recorded at a few sites in London; these are the only known populations in the UK at present. They originate from northern Mexico and southern USA. Red swamp crayfish are crayfish plague carriers. They eat large quantities of water plants as well as small animals and can turn clear lakes into muddy ones that have few or no plants. They burrow much more than Signal crayfish do and they can survive in ditches and shallow ponds that sometimes dry out in summer, where other introduced crayfish could not survive.
White river crayfish (Procambarus acutus) One isolated population has been found in a site near the Thames, which is the only record in the wild for Britain. Initially from the US, this crayfish may have been released accidentally, as a result of stocking a fishery. If it spreads in Britain it may compete with our native crayfish, act as a carrier of crayfish plague and damage river banks by burrowing.