Black-tailed rattlesnake (Crotalus molossus)
The black-tailed rattlesnake is a venomous pit viper in the family Viperidae. GBIF holds 865 licensed U.S. records of it; it reaches our listing threshold in 2 states, most of all Arizona (714) and New Mexico (150). Its observation records peak in August.
The black-tailed rattlesnake (Crotalus molossus) is a venomous pit viper species found in the southwestern United States and Mexico. Four subspecies are currently recognized, including the nominate subspecies described here.
From Wikipedia: Black-tailed rattlesnake, text under CC BY-SA 4.0.
Is the black-tailed rattlesnake poisonous or venomous?
Yes. The black-tailed rattlesnake is a pit viper (family Viperidae), like every rattlesnake, copperhead and cottonmouth in the U.S. Its bite needs emergency care: call 911 and keep the bitten limb still. Antivenom is given in hospital.
Snakes often mistaken for it
Species commonly confused with rattlesnakes and recorded in the same states: gopher snake (recorded in all 2 of its states), plains hog-nosed snake (recorded in all 2 of its states) and Great Plains rat snake (recorded in 1 of its 2 states).
Which states have the black-tailed rattlesnake?
The black-tailed rattlesnake's U.S. record is concentrated: Arizona alone holds 83% of licensed records. It is listed in 2 states in all; the next are New Mexico (150).
GBIF records filed under this name in Texas are counted as the eastern black-tailed rattlesnake, the species that lives there.
| # | State | Records | Share of state snakes | Rank in state |
|---|---|---|---|---|
| 1 | Arizona | 714 | 3.5% | 10th of 60 |
| 2 | New Mexico | 150 | 2.3% | 10th of 56 |
When is the black-tailed rattlesnake seen?
Across the U.S., observation records of the black-tailed rattlesnake run mostly April through September, peaking in August with 40% of them. Almost none are from December to February.
Where the black-tailed rattlesnake is recorded in each state
Arizona
Arizona holds 714 licensed records, the 10th most recorded of 60 snakes listed there. Its observation records in Arizona run mostly April through September, peaking in August; most licensed records come from Cochise County, Pima County and Santa Cruz County. Next come Yavapai County (43) and Maricopa County (39).
New Mexico
New Mexico holds 150 licensed records, the 10th 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 Doña Ana County (14) and Eddy County (14).
Top counties in the U.S.
| # | County | State | Records | Share of U.S. |
|---|---|---|---|---|
| 1 | Cochise County | Arizona | 284 | 32.8% |
| 2 | Pima County | Arizona | 129 | 14.9% |
| 3 | Santa Cruz County | Arizona | 100 | 11.6% |
| 4 | Yavapai County | Arizona | 43 | 5.0% |
| 5 | Hidalgo County | New Mexico | 43 | 5.0% |
| 6 | Maricopa County | Arizona | 39 | 4.5% |
| 7 | Grant County | New Mexico | 34 | 3.9% |
| 8 | Gila County | Arizona | 30 | 3.5% |
| 9 | Graham County | Arizona | 27 | 3.1% |
| 10 | Pinal County | Arizona | 19 | 2.2% |
| 11 | Catron County | New Mexico | 15 | 1.7% |
| 12 | Doña Ana County | New Mexico | 14 | 1.6% |
| 13 | Eddy County | New Mexico | 14 | 1.6% |
| 14 | Greenlee County | Arizona | 13 | 1.5% |
| 15 | Navajo County | Arizona | 11 | 1.3% |
How recent are the black-tailed rattlesnake records?
The black-tailed rattlesnake record leans on older material: only 32% of dated U.S. records come from 2017–2026, and the median record is from 1992. The oldest dated record is from 1893; the busiest year was 2022, with 32 records.
| Decade | Records | Share |
|---|---|---|
| 1890s | 3 | 0.4% |
| 1900s | 4 | 0.6% |
| 1910s | 20 | 2.9% |
| 1920s | 28 | 4.1% |
| 1930s | 56 | 8.2% |
| 1940s | 16 | 2.3% |
| 1950s | 33 | 4.8% |
| 1960s | 63 | 9.2% |
| 1970s | 50 | 7.3% |
| 1980s | 52 | 7.6% |
| 1990s | 45 | 6.6% |
| 2000s | 49 | 7.2% |
| 2010s | 98 | 14.3% |
| 2020s | 166 | 24.3% |
Species recorded in the same counties
Of the 24 counties where the black-tailed rattlesnake is most recorded, 24 are also top counties for the gopher snake, more than for any other snake.
| Species | Shared counties |
|---|---|
| Gopher snake | 24 |
| Ring-necked snake | 23 |
| Glossy snake | 21 |
| Long-nosed snake | 21 |
| Striped whipsnake | 20 |
| Western diamondback rattlesnake venomous | 20 |
| Blackneck garter snake | 19 |
| Coachwhip | 18 |
Related species in the U.S.
Other species of the genus Crotalus with profiles here: Western rattlesnake, Western diamondback rattlesnake, Prairie rattlesnake, Sidewinder, Timber rattlesnake, Mohave rattlesnake, Red diamond rattlesnake and Eastern diamondback rattlesnake.
GBIF records read 2026-09-29. Listed: any license. Counted: CC0/CC BY only. How we count.