Signal Crayfish

The Signal Crayfish is a North American species of Crayfish that has been introduced to Europe and Asia as an invasive species. It was introduced to Europe in the 1960s to bolster crayfish reserves that were being damaged by crayfish plague, however the imports turned out to be a carrier of the plague. They are blue-brown to red-brown in color, with robust, large, smooth claws. They have a white patch near their claw hinge, similar to the white flags that signalmen used for directing trains, from which they derive their name.