Marbled crayfish are mottled blue-green in colour.

Marmorkrebs is German for "marbled crayfish".

Unlike signals, marbled crayfish aren't big enough to eat fish but they can feed on invertebrates such as mayflies which are really important in terms of biodiversity.

Marbled crayfish, thought to be native to North America, are banned in the UK because of the severe threat which they pose to native wildlife and the environment.

The National Wildlife Crime Unit has recovered about a dozen marbled crayfish from home aquariums at three properties in the Central Belt, Scotland on Sunday can reveal.

They are large and slow-growing, and are threatened by habitat loss, overexploitation by local people and by spread of introduced non-indigenous Marbled crayfish (Procambarus fallax f. virginalis).

The NWCU was alerted to the potential for illegal trading by UK government agency the Centre for Environment, Fisheries and Aquaculture Science (CEFAS), which noticed an advertisement for marbled crayfish online.

The biggest difference between marbled crayfish and other crayfish species is that the others need a male and a female to reproduce, but marbled crayfish are parthenogenic [reproduce asexually] which means you only need one to establish a population.