Signal Crayfish

The signal crayfish is a freshwater crayfish native to rivers, lakes, and streams of the Pacific Northwest of North America. It is identified by a smooth, robust body and a small white or pale turquoise patch at the hinge of each claw, the mark that gives the species its common name. Introduced widely to Europe, the United Kingdom, and Japan during the twentieth century for aquaculture, it has become one of the most damaging invasive crayfish species outside its native range. It carries a fungal pathogen known as crayfish plague without being harmed by it, while spreading the disease to native crayfish species that have no resistance and die in large numbers on contact. In its introduced range it also burrows aggressively into riverbanks, damaging banks and levees, and outcompetes native crayfish for food and shelter. Within its native Pacific Northwest range, by contrast, it lives as an unremarkable and ecologically balanced part of the freshwater community.