Pacifastacus leniusculus is quite large (12-20 cm) and weighs on average 50 g (up to 200 g). The upper part of the signal crayfish's body is of a color that varies between red, brown and gray. It is easily recognizable due to the white (or sometimes bluish) spot present on the claws. The underside of the claws has a bright red coloration.
Did you know?
Signal crayfish is the most abundant crayfish in Luxembourg, it has colonised a large part of the aquatic environment since its introduction (probably in the 1970s). Like other invasive crayfish (e. g. red swamp crawfish, Procambarus clarkii) it was introduced for gastronomic purposes, but this proved to be a disaster for indigenous crayfish in particular. In Luxembourg this action resulted in the disappearance of stone crayfish (Austropotamobius torrentium) and the near disappearance of the European crayfish (Astacus astacus) due to, among other things, the transmission of the crayfish plague. Today it affects other native species such as the thick-shelled river mussel.