Snake identification sometimes requires close examination of obscure details. For example, that's a garter snake at the right. However, in North America there are several look-alike garter snake species, plus ribbon snakes look a lot like garter snakes. Therefore, if we want to be sure we really have the Common Garter Snake, Thamnophis sirtalis, we need to make decisions on such obscure characteristics as those referred to below. Here are the Common Garter Snake's main field marks:
SNAKE HEAD SCALE NAMES (A Coachwhip, not a Garder Snake)
COMMON GARTER SNAKES
Common Garter Snakes are small snakes, usually only a couple of feet long, but capable of being much longer. Long stripes extend from head to tail, so they don't look at all like any venomous species in North America. Though they are peaceful creatures content to eat frogs, toads, earthworms, mice and even fish, if you mishandle them they'll try to bite you. If you manage to hold one's head so it can't bite, it wraps its body around your arm, smearing you with a very disagreeably smelling musk.
Common Garter Snakes have 7 upper lip-scales or supralabials. (This shows that in critical places, especially on the head, even individual scales may be numbered!
Garter snake anal plates -- the large scale or scales next to the anus, at the end of the broad belly plates -- are single. (Anal plates are also important when identifying groups of snakes. Garter snakes, king snakes, and pit vipers, for instance, have single anal plates, but in the water snakes, racers, and rat snakes, the plates are divided.) At the left you see a rat snake's divided anal plate. The pinkish slit running horizontally across the snake's bottom is its cloaca, which is like an anus except that it has more functions. The snake's tail extends toward the upper right. Notice the diagonal, irregular fissure across the scale below the cloaca, thus on the "head side" of the cloaca. That fissure divides the anal plate, so this is a good example of a divided anal plate. The scale in the same place on a garter snake wouldn't have that fissure because garter snakes have single anal plates.