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:
- On the Common Garter Snake, each side
stripe is confined to the 2nd and 3rd scale rows (except in Texas). (This shows that in
snakes the scales don't grow randomly, like
hairs on a human body; they occur in rows, and each row is numbered.
At the right you see the shed skin of a Racer, Coluber constrictor clearly
showing each individual scale. )
- Between the stripes there are often red blotches or a double row of alternating black
SNAKE HEAD SCALE NAMES (not a Garder Snake)
- Common Garter Snakes have 19 rows of scales along the side of the body
- Garter snake have keeled scales, which means that each individual scale
has a narrow ridge running down its middle. (This is an important feature when
identifying groups of snakes.
- Garter snakes and water snakes have keeled scales
- rat snakes have weakly keeled scales
- king snakes and racers have "smooth" scales.)
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 anus,
with the snake's tail beyond the upper right. Notice the diagonal, irregular fissure
across the scale below the anus, thus on the "head side" of the anus. 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.