hoop snake

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Any of several snakes, such as the mud snake, said to grasp the tail in the mouth and move with a rolling, hooplike motion.

Wiktionary

1. n. A mythical creature of the United States and Australia, a snake that grasps its tail in its jaws and thereby rolls after its prey like a wheel.

GNU Webster's 1913

1. n. (Zoöl.) a harmless snake of the Southern United States (Abaster erythrogrammus); -- so called from the mistaken notion that it curves itself into a hoop, taking its tail into its mouth, and rolls along with great velocity.

WordNet 3.0

1. n. any of various harmless North American snakes that were formerly believed to take tail in mouth and roll along like a hoop