Crotalus molossus
Silhouette: Bill Bouton (source photo) & T. Michael Keesey (vectorization) · PhyloPic
In 3 days ~40% in a week ~70%
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.
A 2012 revision showed that eastern populations from Texas and central and eastern New Mexico form a distinct species separate from C. molossus: Crotalus ornatus Hallowell 1854. Alternate common names are green rattler, and Northern black-tailed rattlesnake.
This medium-sized species averages from 76 to 107 cm (30 to 42 in) in length. The females tend to be larger than the males. They range in color from yellows and olive greens to browns and black. As their name implies, one of their most distinguishing features is, despite variations in body color, entirely black tail scales. Often, this rattlesnake has a black band across its eyes extending diagonally down to the corners of its mouth... Wikipedia →
Recording0:10
United States · 2025
© Christian Schwarz · iNaturalist · CC BY-NC 4.0
Recording0:22
United States · 2021
© BJ Stacey · iNaturalist · CC BY-NC 4.0
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Saguaro National Park | 🇺🇸 United States | |
| 2 | Cumbres de Monterrey National Park | 🇲🇽 Mexico |
| # | City | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Mexico City | 🇲🇽 México | |
| 2 | Mesa | 🇺🇸 United States |
| # | Zoo / Centre | Country | |
|---|---|---|---|
| 1 | Skansen | 🇸🇪 Sweden | |
| 2 | Greensboro Science Center | 🇺🇸 United States | |
| 3 | Zoo Miami | 🇺🇸 United States | |
| 4 | Ecological Center of Sonora | 🇲🇽 Mexico | |
| 5 | Sedgwick County Zoo | 🇺🇸 United States | |
| 6 | Parque Zoológico de León - Zooleón | 🇲🇽 Mexico | |
| 7 | Phoenix Zoo | 🇺🇸 United States | |
| 8 | Louisville Zoo | 🇺🇸 United States | |
| 9 | Zoológico Benito Juárez | 🇲🇽 Mexico | |
| 10 | Arizona-Sonora Desert Museum | 🇺🇸 United States | |
| 11 | ABQ BioPark Zoo | 🇺🇸 United States | |
| 12 | Cameron Park Zoo | 🇺🇸 United States | |
| 13 | Philadelphia Zoo | 🇺🇸 United States | |
| 14 | Chapultepec Zoo | 🇲🇽 Mexico | |
| 15 | Schönbrunn Zoo | 🇦🇹 Austria | |
| 16 | Pittsburgh Zoo & Aquarium | 🇺🇸 United States | |
| 17 | Riverbanks Zoo | 🇺🇸 United States | |
| 18 | Reptile Gardens | 🇺🇸 United States | |
| 19 | Oregon Coast Aquarium | 🇺🇸 United States | |
| 20 | Rancho Mágico | 🇲🇽 Mexico | |
| 21 | Staten Island Zoo | 🇺🇸 United States | |
| 22 | Parque museo La Venta | 🇲🇽 Mexico | |
| 23 | Hatfield Visitors Center | 🇺🇸 United States | |
| 24 | Baltic Sea Science Center | 🇸🇪 Sweden |
Possible
About 20% of wildlife watchers report a Western Black-tailed Rattlesnake sighting in Saguaro National Park on a given day, based on 78 verified sightings from GBIF citizen-science data from 2019 to 2026. It is the 19th most-seen of the 51 reptiles we can rate there. Over three days the chance rises to about 40%, and over a week to about 70%, if each day is a fresh chance.
August and September
In those months about 30% of wildlife watchers report a Western Black-tailed Rattlesnake in Saguaro National Park on a given day, against under 5% in January–February and June, the lowest months. Those are among Saguaro National Park's wettest months, with about 45 mm of rain a month against almost none in May.
Between 10 am and 1 pm
Across all the parks we cover, that three-hour window holds the most Western Black-tailed Rattlesnake sightings with a recorded time, and about 6 in 10 of them come between 6 am and 6 pm: it is seen both by day and at night.
Yes
Of the 2 parks where we can rate Western Black-tailed Rattlesnake sightings, Saguaro National Park has the highest daily chance: about 20%. Next come Cumbres de Monterrey National Park (Mexico, under 5%).
Same genus: Crotalus
The closest relatives of the Western Black-tailed Rattlesnake that you can see in Saguaro National Park (genus Crotalus, Rattlesnakes) are Western Diamondback Rattlesnake (about 40%), Tiger Rattlesnake (about 20%) and Arizona Black Rattlesnake (about 10%), with each one's daily chance of a sighting.
GBIF citizen-science records
It is estimated from how often the Western Black-tailed Rattlesnake is recorded against all the reptiles logged in Saguaro National Park (78 verified sightings from 2019 to 2026), calibrated against known sighting rates. Figures are rounded to the nearest 10% because citizen-science data supports honest approximations, not decimals, and months with records from fewer than five people show "—". How it works.
