Freshwater white-clawed crayfish  (Austropotamobius pallipes)

The only freshwater crayfish native to the UK (3), this species is olive-green to brown in colour and can reach up to 12 centimetres in length. The common name refers to the fact that the undersides of the claws are off-white to pinkish in colour. Females tend to have wider abdomens than males, and males have larger claws. In males, the first two appendages are specialised; they are used to place a sperm mass (spermatophore) underneath the female during mating (2).