Faxonius immunis is a species of crayfish in the family Cambaridae. It is native to North America and it is an introduced species in Europe, where it lives along the Upper Rhine. Its common names include calico crayfish and papershell crayfish.
Faxonius immunis is similar to a number of species of crayfish in the genus Faxonius. While the colouration of the claws is distinctive, it can be difficult to use that to identify a specimen without reference specimens for comparison. F. immunis can be distinguished from F. virilis by the presence of a notch near the base of the dactylus (finger) of the claw, which is not found in F. virilis.
Faxonius immunis is only found in slow-flowing bodies of water, such as streams, ponds, marshes and roadside ditches, in contrast to F. virilis which also lives in rivers with moderate flow. It can survive in areas with large fluctuations in the amount of available water, by burrowing into the ground when the surface waters recede.
