It is quite a claim to fame to be the least wanted species in Europe but the red swamp crayfish, Procambarus clarkii, seems to have that distinction. It was picked out as a major threat to other wildlife, riverbanks and ponds in 14 countries to illustrate the efforts of a new Europe-wide organisation trying to eliminate alien species.
So far this native of North America has only been found at 16 locations in England, including the ponds on Hampstead Heath in London, and more ominously in the Grand Union canal, which could give the crayfish access to a large part of the country.
Not that the swamp crayfish needs water to survive; it can travel overland, live in oxygen-poor and saline environments, and although only 90mm (3.5in) long is aggressive when approached. It burrows deep into banks causing leaks in canals and dams. It also carries the crayfish plague so is a big threat to the native white-clawed crayfish as well as outcompeting it for food.
The swamp crayfish breeds in spring and lays up to 600 eggs so spreads rapidly, eating plants, small fish, amphibians and other available creatures. Fortunately, herons, foxes and eels will eat these invaders while scientists try to slow their spread and seek a way of eliminating them.
