India, Oct. 29 -- A frog introduced for hunting and food has become a threat to one of Arizona's native snakes. A U.S. Fish and Wildlife Service species assessment traces bullfrogs' arrival in Arizona to 1926, following a systematic introduction effort by the State Game Department to provide opportunities for sport hunting and a source of food. The assessment identifies nonnative species, particularly bullfrogs, crayfish, and sport fish, as major threats to the northern Mexican garter snake, which the document estimates occupies only about 10% of its historical habitat.

The northern Mexican garter snake can be easy to overlook. It is olive to olive-brown in color, has three stripes across its body, and can grow up to 44 inches long. It p...