Signal crayfish

Signal crayfish
	;
Conservation status
	; Least Concern
Scientific classification
Kingdom:	Animalia;
Phylum:	Arthropoda;
Subphylum:	Crustacea;
Class:	Malacostraca;
Order:	Decapoda;
Superfamily:	Astacoidea;
Family:	Astacidae;
Genus:	Pacifastacus;
Species:	P. leniusculus;
Binomial name
	Pacifastacus leniusculus; (Dana, 1852)

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The signal crayfish, Pacifastacus leniusculus, is an American crayfish indigenous to the western United States.^[1] Members of this species are up to 15 cm in length.^[2] They are bluish-brown to reddish-brown in color with robust large smooth claws. They have a white patch near the claw hinge.^[2] Like all crayfish, they are solitary animals and are omnivorous, although their diet is mainly vegetarian they will eat anything from decaying roots and leaves to meat, including crayfish smaller than themselves.^[3]

Due to the crayfish plague that ravaged European crayfish stocks and has almost exterminated the noble crayfish Astacus astacus, the Swedish biologist Gunnar Svärdson went to the US to search for a crayfish that could replace the native European crayfish. He found the signal crayfish and started to introduce it into Swedish rivers and lakes. This was the beginning of the introduction of this crayfish not only to various European countries but also to Japan. It was Svärdson who named the signal crayfish. He observed how they were in the habit of waving their claws and thought that the white patches made them look like train dispatchers signaling to an engineer.

Unfortunately, this crayfish has been carelessly introduced to various countries without considering the fact that it carries the crayfish plague, and thus causes the eventual extermination of native crayfish. This was the case both in Great Britain and in Japan.