| 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 Massasauga |
| 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 Bullsnake |
| 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 Coachwhip |
| 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 Racer |
| 25b. | Body bright grass green; nostril centered in single scale. | Opheodrys vernalis Smooth green snake |