How to identify it
Olive-gray to brown back, gray or bluish-gray head, whitish to greenish or brownish belly; adults 41-71 cm (rarely to 109 cm). [1][2]
Yellow to white mid-dorsal stripe, shading to orange toward the head, separating two black blotches, one on each side of the neck. [1][2]
Two rows of alternating dark spots between the stripes give a checkerboard look; lateral stripes (cream, tan or yellow) on scale rows 2 and 3. [1][2]
19 rows of keeled dorsal scales; juveniles are brighter and more contrasting than adults. [1][2]
Compared with the checkered gartersnake (thamnophis marcianus): Checkered gartersnake has 21 rows of keeled dorsal scales, a pale-yellow crescent behind the head and a single thick black neck line, versus 19 rows and two black neck blotches in the black-necked. [1][2]
Species it is confused with
Check these before deciding what you are looking at. If you are not certain what it is, do not shoot.
- Checkered gartersnake · Thamnophis marcianus
Field notes
- Identification Confirm a black-necked gartersnake before you act. Compared with the checkered gartersnake (thamnophis marcianus): Checkered gartersnake has 21 rows of keeled dorsal scales, a pale-yellow crescent behind the head and a single thick black neck line, versus 19 rows and two black neck blotches in the black-necked.[1][2]
Where it lives
Streams in valleys and canyons and shallow rocky pools, also riparian woodland, pine-oak forest, scrub, desert flats and dry grassland; may use cattle tanks as water recedes. [1][2]
How it behaves
Semi-aquatic and most active by day, though night activity is not unusual; if threatened it flees into cover or water, flattens and broadens its head, and releases foul-smelling musk. [1][2]
Eats mainly frogs, toads and tadpoles, plus small fish, skinks, crustaceans and earthworms; forages actively in spring when water and prey are abundant and uses sit-and-wait ambush in summer. [1][2]
At night shelters in exposed roots along stream banks, crevices, rodent holes and debris; hibernates in winter dens. [1][2]
Limited legal take
Legal take of this species exists only under narrow conditions — a quota, a draw, a permit, a small area, or animals released or held on private land — set by the authorities below. Nowhere else is a legal opportunity implied, and Hunt shows one only where a certified rule establishes it.
Where legal take is listed
- Utah — reptile take · Reptile and amphibian species classification tables (R657-53), updated Apr. 22, 2026
Being listed is not an open season. Seasons, zones, licences, methods and limits decide whether this animal may be taken on a given day and place — check Hunt or the authority before you go. Listings read 2026-09-30.
Where it is found
Southern Colorado, southwestern Utah, central and eastern Arizona, New Mexico (except the far east) and western and central Texas, south through Mexico to Guatemala. Not in Canada.
Sources
Every claim above is attributed to one of these published sources.
NatureServe · reviewed 2026-09-30
NatureServe
University of Michigan Museum of Zoology · reviewed 2026-09-30
University of Michigan Museum of Zoology