Alien species of crayfishes – American and signal crayfishes are invasive species. They pose a threat to indigenous species because they may displace natives due to intraspecific competition or due to spreading of lethal disease for European crayfishes, called crayfish plague. Therefore it is forbidden to release alien crayfish species if we acquire them. We may take along these invasive species and cook them for the repast. If we have no such possibilities, then the best and most humanitarian way of putting them to death is freezing. However before we will take any action, first we have to know how to identify the species of those crustaceans as totally different procedures apply to particular species of crayfishes.