The signal crayfish is a freshwater crustacean native to North America. It is recognized by its large size, typically reaching up to 15 cm in length, and its distinctive blue-green color with red markings on the claws. These crayfish inhabit rivers, lakes, and ponds, preferring areas with plenty of hiding spots like rocks and vegetation. Introduced to Europe in the 1970s for aquaculture, the signal crayfish has since become an invasive species in many regions. Its presence threatens native species, such as the white-clawed crayfish, by competing for resources and spreading diseases. Conservation efforts are ongoing to manage its impact on local ecosystems.