Colorado Herpetological Society
Colorado's Snakes
by Lauren J. Livo
Evaluate the criteria below to identify a species.

1a. Rattle present at end of tail. go to 2
1b. No rattle present. go to 3
2a. Numerous small scales on top of head, maximum total length about 4'. Crotalus viridis
Western (prairie) rattlesnake
2b. Head covered by large scales, maximum total length about 2'. Sistrurus catenatus
3a. Stripes running the length of the body. go to 4
3b. Body plain, banded, or blotched, but without longitudinal stripes. go to 9
4a. Scales smooth; longitudinal black and white stripes. Masticophis taeniatus
Striped whipsnake
4b. Scales keeled. go to 5
5a. Distinct black bars at edge of scales on upper lips. go to 6
5b. Not as above. go to 7
6a. Pale stripe on side of body on 3rd and 4th scale rows above belly scales. Thamnophis radix
Plains garter snake
6b. Pair of glossy black blotches behind head; pale stripe on side of body on 2nd and 3rd scale rows above belly scales. Thamnophis cyrtopsis
Blackneck garter snake
7a. Red color on sides. Thamnophis sirtalis
Common garter snake
7b. No red color on sides. go to 8
8a. Belly with conspicuous double row of half-moon markings. Tropidoclonion lineatum
Lined snake
8b. Belly variable, but without half-moon markings. Thamnophis elegans
Western terrestrial garter snake
9a. Body with distinctly keeled scales. go to 10
9b. Scales on body smooth or very weakly keeled. go to 13
10a. Nose distinctly upturned. go to 11
10b. Not as above. go to 12
11a. Well-ordered, circuluar spots running head to tail with a single dark horizontal stripe connecting the eyes and a light stripe immediately above it. Heterodon nasicus
Western hognose snake
11b. Spots blotchy and less pronounced, or absent entirely. Head darker with dark markings extending several inches down back.
12a. Single anal scale; background color yellowish with brown blotches. Pituophis catenifer
12b. Divided anal scale; brown bands on brown or tan body (pattern may be obscured in old individuals). Nerodia sipedon
Northern water snake
13b. Scales on back very weakly keeled; body tan with brown blotches; rectangular marks on belly; dark stripes on underside of tail. Elaphe guttata
Corn snake
13b. Scales completely smooth; body pattern variable. go to 14
14a. Body with red, black, and cream (or yellow) pattern. go to 15
14b. Pattern not as above. go to 16
15a. Band pattern on body of cream - black - red - black - cream. Lampropeltis triangulum
Milk snake
15b. Pattern of red and black bands with cream speckling. Rhinocheilus lecontei
Longnose snake
16a. Pattern of brown blotches on paler background. go to 17
16b. Pattern not as above. go to 18
17a. Single anal scale; length to 56 inches. Arizona elegans
Glossy snake
17b. Divided anal scale; vertical pupils; small size (adult length less than 20 inches). Hypsiglena torquata
Night snake
18a. Tan body, black head, small size (adults less than 15 inches). go to 19
18b. Not as above. go to 20
19a. Eastern slope. Tantilla nigriceps
Plains blackhead snake
19b. Western slope. Tantilla hobartsmithi
Southwestern blackhead snake
20a. Pattern of black and white bands or black with white speckling. Lampropeltis getula
Common kingsnake
20b. Not as above. go to 21
21a. Tail resembles braided whip; adults large (to 80 inches). Masticophis flagellum
21b. Tail plain, not resembling braided whip. go to 22
22a. Olive body with orange ring around neck. Diadophis punctatus
Ringneck snake
22b. Not as above. go to 23
23a. Worm-like appearance, with dorsal and ventral scales about the same size, vestigial eyes. Leptotyphlops dulcis
Texas blind snake
23b. Not as above. go to 24
24a. Body variable (orange, brown, or gray), often with dark saddles; maximum total length about 15 inches. Sonora semiannulata
Ground snake
24b. Not as above. go to 25
25a. Olive or brownish body with yellow or cream belly; nostril bordered by two separate scales. Coluber constrictor
25b. Body bright grass green; nostril centered in single scale. Opheodrys vernalis
Smooth green snake