A rattlesnake that looks like a rock. This Southwestern Speckled Rattlesnake was found in central Arizona in an area of rusty granite and quartz. The resulting cryptic pattern is just as colorful, including speckled grey blue eyes. Though it is brightly colored, these snakes can be very difficult to see in context.
Crowell, H. L., Whelan, J. M., & Harmel, M. V. (2020). Rattlesnake colouration affects detection by predators. Journal of Zoology, 310(1), 1–11. https://doi.org/10.1111/jzo.12786
Hanscom, R. J. (2025). From ambush to activity: Using accelerometry to reveal cryptic behaviors of rattlesnakes and kangaroo rats [Doctoral dissertation, University of California, Riverside]. eScholarship. https://escholarship.org/content/qt4ft2985w/qt4ft2985w.pdf
A Southwestern Speckled Rattlesnake in ambush on a humid night a couple of years back. Like many other desert reptiles, the monsoon and period after are the most active times of year. Humid air and cooler, stable temperatures make for safer activity, and a lot has to be done in a relatively short amount of time.
A Southwestern Speckled Rattlesnake hanging out in the shade on a blistering hot morning several years ago. This snake is still using this spot in the summer, staying cooler during the day and emerging at night, staying very near.
This is why, when we are called to capture a snake at a home during peak summer, we search for others. Especially without rain, they’re tethered to aestivation sites, never going far. If a rattlesnake is found on the back patio right now, there are only a few possibilities. It was either displaced by construction, tossed over the fence by the fire department, or it has been there for several weeks, successfully hiding as it always has before being discovered.
A Southwestern Speckled Rattlesnake resting along the top of a drainage after a night out. During the summer months, these and other rattlesnake species are primarily nocturnal, being encountered by people mostly in the hour before and after sunrise. As soon as the sun reaches the area, these snakes make a beeline for their aestivation sites to hide for the day.
The fact that rattlesnakes are often nocturnal and that they spend much of their lives avoiding excess heat is a surprise to many people. The misconception is that reptiles, ectotherms who get heat from the environment rather than produce it themselves, want it hot … the hotter the better. You’ll see this soon, in the form of comments like “it’s getting hot! It brings the rattlers out”, warnings from fire departments, and even articles in local news when temperatures stabilize in the triple digits for the year.
But thermoregulation means being the right temperature, not just as hot as possible. In fact, a body temperature sustained above around 105˚F can kill a rattlesnake. Interestingly, the upper terminal temperature seems to be similar across rattlesnake species, regardless of the environment they’re found. It’s often over 100˚F when these snakes begin their move back to their underground hiding spots, meaning they ride the line of death very closely, staying out as long as possible for the chance to find prey. If they are disturbed during this crawl for too long, or escape into the wrong hiding spot, it can quickly kill them.
We have learned this first-hand, unfortunately, from finding snakes within our study area who were first found by snake enthusiasts, likely mid-crawl. Thanks to Instagram, individual snakes that had died this way can be tied to individual events where a prolonged photo session and subsequent release of a heat-stressed snake resulted in death. To some herpers, it may seem like gatekeeping to discuss this kind of thing, but dead snakes are a lesson to those who would hear it.
During the summer, you may see us be critical of snake relocations performed by the fire department, and well-meaning individuals. This comes from the practice of releasing these snakes to improper cover, where they will be very unlikely to find survivable conditions in time. Every time you see a video of someone releasing a snake to open ground or random creosote mid-day, the relocator watches it crawl away and may be satisfied that they helped the animal … but these snakes do not survive for long.
Claunch, N. M., Lind, C. M., Lutterschmidt, D. I. (2023). Stress ecology in snakes. In Penning, D. A. (Ed.), The Stress Ecology of Reptiles. ResearchGate.
Cadena, V., Andrade, D. V., Bovo, R. P., Tattersall, G. J. (2013). Evaporative respiratory cooling augments pit organ thermal detection in rattlesnakes. Journal of Comparative Physiology A, 199(9), 883–893.
https://doi.org/10.1007/s00359-013-0852-4
Castro, S. A., Prado, J. V., Wang, T. (2024). The relevance of vascular adjustments to hemodynamic control in the face of temperature change in Crotalus durissus. Journal of Experimental Biology, 227(15).
Laursen, W. J., Anderson, E. O., Hoffstaetter, L. J., Bagriantsev, S. N., & Gracheva, E. O. (2015). Species-specific temperature sensitivity of TRPA1. Temperature, 2(1), 142–157.
https://doi.org/10.1080/23328940.2014.1000702
Kamees, L. K. (2022). Competing Behaviors of Thermoregulation and Ambush Foraging in the Timber Rattlesnake (Crotalus horridus horridus): A Mechanistic Assessment of Thermal Behavior (Doctoral dissertation, University of Arkansas).
https://scholarworks.uark.edu/etd/5172
Tattersall, G. J., Sinclair, B. J., Withers, P. C., Fields, P. A., Seebacher, F., Cooper, C. E., & Maloney, S. K. (2012). Coping with thermal challenges: physiological adaptations to environmental temperatures. In Comprehensive Physiology, Wiley.
LaDuc, T. J., Borrell, B. J., & Dudley, R. (2005). Respiratory cooling in rattlesnakes. Comparative Biochemistry and Physiology Part A, 141(4), 509–516.
https://doi.org/10.1016/j.cbpb.2005.04.010
Carnes-Mason, M. D., & Beaupre, S. J. (2025). Temperature manipulation induces ecdysis in lab-held rattlesnakes. Ichthyology & Herpetology, 113(2), 274–281.
A Southwestern Speckled Rattlesnake rests in a rocky retreat, waiting for dark. Like other rattlesnake species in the Phoenix area, once temperatures stabilize in the triple digits, their activity becomes mostly nocturnal. The late afternoon is a good time to wait for a lizard or bird to make a mistake, in the meantime.
A Southwestern Speckled Rattlesnake resting in the shade outside its summer aestivation den. It’s one of a handful that gather here each year to hide from the heat and gestate.
A Southwestern Speckled Rattlesnake from a mountain range in western Arizona. This is one of a couple seen on a sunrise hike on what would be a very hot day. It was spotted crossing a wash from a sandy rise in the center, where it had likely spent the night in ambush. As temperatures approached 100˚F at around 7am, this snake needed to get to deep cover, and it knew right where to go.
A Southwestern Speckled Rattlesnake as they typically appear around Camelback Mountain in central Phoenix. It’s a surprise to many that multiple species of rattlesnakes are still present within a heavily populated urban area, but they continue to thrive there. Excessive heat from a surrounding sea of pavement makes life difficult in the summer, however, which often leads to encounters at adjacent homes with rattlesnakes looking to cool off in the lawns and citrus oasis of Paradise Valley.
