A garter snake.
garter snake definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
any of various small, harmless, striped colubrid snakes (genus Thamnophis) common in North America
garter snake definition by American Heritage Dictionary
Any of various nonvenomous North and Central American snakes of the genus Thamnophis, having longitudinal stripes.