A highly aggressive and voracious predator (3), the signal crayfish is known to grow large enough to predate on some fish species (9), including the bullhead (Cottus gobio) and stone loach (Barbatula barbatula) in Britain (3) (10). In addition, the signal crayfish feeds on frogs and invertebrates, and has even been recorded eating individuals of its own species (3) or occasionally feeding on nematode worms (7). Although the signal crayfish tends to show a preference for consuming animals (8), this species is omnivorous, and so also eats vegetation (2) (3).
The signal crayfish is a nocturnal species (2), and is known to take shelter under rocks and boulders, within tree roots or in burrows and cavities within banks (6). In the winter, adult signal crayfish shelter in burrows and enter a state of torpor. These burrows are formed of many inter-connecting tunnels, and can be up to two metres deep (5).
The signal crayfish is an extremely successful competitor, particularly within its introduced habitats. A large and hardy species (10), the signal crayfish is more active and aggressive than other crayfish, and often has larger pincers. In addition, this species is thought to be able to tolerate relatively high temperatures, and may also be less vulnerable to winter conditions than native crayfish species (2).
The signal crayfish has a relatively high reproductive potential (2), with the female of this species laying between 200 and 400 eggs in the autumn (3) (5). The female then carries the eggs around under her tail through the winter until the spring (3) (5), when the eggs hatch (5). Once hatched, the young remain attached to the female’s tail until they are released in May or June (5). Signal crayfish reach sexual maturity at about 2 or 3 years old (5), and can live for up to 20 years (3) (5).
The signal crayfish is known to grow faster than any of the native European crayfish species (2) (4). It was this quality, in addition to its resistance to crayfish plague, which made the signal crayfish an attractive commercial species and a popular replacement for disease-ravaged native crayfish populations in Europe (4) (10). Unfortunately, the signal crayfish is a carrier of crayfish plague, and is thought to be responsible for passing the deadly disease to the white-clawed crayfish (Austropotamobius pallipes) in the UK (3).
In the UK, the signal crayfish is known to be predated by otters (Lutra lutra), American mink (Mustela vison) and predatory fish such as Atlantic salmon (Salmo salar) and European eels (Anguilla anguilla) (5).