Blackneck garter snake (Thamnophis cyrtopsis)
The blackneck garter snake is a snake in the family Colubridae with a mild venom for its prey, not dangerous to people. GBIF holds 1,417 licensed U.S. records of it; it reaches our listing threshold in 5 states, most of all Arizona (758), Texas (438) and New Mexico (206). Its observation records peak in August.
Common names: blackneck garter snake, black-neck garter snake Thamnophis cyrtopsis, the blackneck garter snake, is a species of garter snake of the genus Thamnophis. It is native to the southwestern United States, Mexico and Guatemala, and can be found in a wide range of different habitats, often near water sources.
From Wikipedia: Blackneck garter snake, text under CC BY-SA 4.0.
Is the blackneck garter snake poisonous or venomous?
Mildly venomous but not dangerous: the blackneck garter snake has enlarged rear teeth and a mild venom for its prey, and a bite causes at most local swelling, which is why many sources simply call it harmless. It is not a pit viper or coral snake, the only U.S. land snakes with medically dangerous venom. Clean any bite like a small wound.
Which states have the blackneck garter snake?
The blackneck garter snake's U.S. record is concentrated: Arizona alone holds 53% of licensed records. It is listed in 5 states in all; the next are Texas (438), New Mexico (206) and Utah (12).
| # | State | Records | Share of state snakes | Rank in state |
|---|---|---|---|---|
| 1 | Arizona | 758 | 3.7% | 7th of 60 |
| 2 | Texas | 438 | 1.1% | 27th of 86 |
| 3 | New Mexico | 206 | 3.2% | 8th of 56 |
| 4 | Utah | 12 | 0.4% | 21st of 28 |
| 5 | Colorado | 2 | 0.1% | 24th of 26 |
When is the blackneck garter snake seen?
Across the U.S., observation records of the blackneck garter snake run mostly April through October, peaking in August with 28% of them. Almost none are from December to February.
Season by state
Among states whose main season falls within one calendar year, it starts earliest in March (Texas) and latest in July (Arizona). Each of these states peaks in a different month: May in Texas and August in Arizona.
| State | Main season | Peak month | Observation records |
|---|---|---|---|
| Texas | March through September | May | 94 |
| Arizona | July through October | August | 87 |
Where the blackneck garter snake is recorded in each state
Arizona
Arizona holds 758 licensed records, the 7th most recorded of 60 snakes listed there. Its observation records in Arizona run mostly July through October, peaking in August; most licensed records come from Pima County, Cochise County and Santa Cruz County. Next come Maricopa County (50) and Yavapai County (47).
Texas
Texas holds 438 licensed records, the 27th most recorded of 86 snakes listed there. Its observation records in Texas run mostly March through September, peaking in May; most licensed records come from Brewster County, Travis County and Jeff Davis County. Next come Presidio County (43) and El Paso County (28).
New Mexico
New Mexico holds 206 licensed records, the 8th most recorded of 56 snakes listed there. Most of its licensed records in New Mexico come from Hidalgo County, Grant County and Catron County. Next come Santa Fe County (20) and Eddy County (15).
Top counties in the U.S.
| # | County | State | Records | Share of U.S. |
|---|---|---|---|---|
| 1 | Pima County | Arizona | 223 | 15.7% |
| 2 | Cochise County | Arizona | 142 | 10.0% |
| 3 | Santa Cruz County | Arizona | 133 | 9.4% |
| 4 | Brewster County | Texas | 76 | 5.4% |
| 5 | Travis County | Texas | 68 | 4.8% |
| 6 | Jeff Davis County | Texas | 60 | 4.2% |
| 7 | Maricopa County | Arizona | 50 | 3.5% |
| 8 | Yavapai County | Arizona | 47 | 3.3% |
| 9 | Gila County | Arizona | 47 | 3.3% |
| 10 | Graham County | Arizona | 43 | 3.0% |
| 11 | Hidalgo County | New Mexico | 43 | 3.0% |
| 12 | Presidio County | Texas | 43 | 3.0% |
| 13 | Grant County | New Mexico | 34 | 2.4% |
| 14 | Catron County | New Mexico | 33 | 2.3% |
| 15 | El Paso County | Texas | 28 | 2.0% |
How recent are the blackneck garter snake records?
The blackneck garter snake record leans on older material: only 15% of dated U.S. records come from 2017–2026, and the median record is from 1969. The oldest dated record is from 1873; the busiest year was 1950, with 32 records.
| Decade | Records | Share |
|---|---|---|
| 1870s | 11 | 1.0% |
| 1890s | 3 | 0.3% |
| 1900s | 9 | 0.8% |
| 1910s | 45 | 4.1% |
| 1920s | 55 | 5.0% |
| 1930s | 92 | 8.4% |
| 1940s | 66 | 6.0% |
| 1950s | 123 | 11.2% |
| 1960s | 152 | 13.8% |
| 1970s | 128 | 11.7% |
| 1980s | 71 | 6.5% |
| 1990s | 42 | 3.8% |
| 2000s | 72 | 6.6% |
| 2010s | 88 | 8.0% |
| 2020s | 141 | 12.8% |
Species recorded in the same counties
Of the 35 counties where the blackneck garter snake is most recorded, 31 are also top counties for the gopher snake, more than for any other snake. Venomous species among its neighbors: the western diamondback rattlesnake.
| Species | Shared counties |
|---|---|
| Gopher snake | 31 |
| Striped whipsnake | 28 |
| Western diamondback rattlesnake venomous | 27 |
| Eastern patch-nosed snake | 25 |
| Glossy snake | 25 |
| Long-nosed snake | 24 |
| Ring-necked snake | 24 |
| Coachwhip | 23 |
Related species in the U.S.
Other species of the genus Thamnophis with profiles here: Western terrestrial garter snake, Common garter snake, Western ribbon snake, Aquatic garter snake, Northwestern garter snake, Western aquatic garter snake, Plains garter snake and Checkered garter snake.
GBIF records read 2026-09-29. Listed: any license. Counted: CC0/CC BY only. How we count.