ZTZTZTZTZTZTZTZTZTZTCHITCHITCHIT, chit, chit, tet, tet!!! The now familiar sound of a buzzing rattlesnake comes from the ground at my feet and all I can do is freeze in place. I cannot see the snake, as it is now several hours after dark, the sky is overcast, and both my headlamp and cellphone batteries are dead. Now that it has fallen silent, I can only guess whether it is still sitting at my feet, coiled and ready to strike, or like others so far, it is already slithering away to safety. I’m wearing light tennis shoes and shorts, and I’m extremely aware of the nakedness of my lower legs.
It’s the first night after the first monsoon storm of the summer, and it seems that all the rattlesnakes in this canyon have come out to soak in the humid warmth and look for mates. This is already the sixth rattlesnake I’ve quite literally stumbled upon in the dark. I’ve been walking slow due to the lack of light, and each snake has waited until I was within a meter’s distance before raising their alarm: it has made for a rather harrowing night hike.
Despite the adrenaline dump my body has produced in response to the sound of each snake’s rattle this evening, I can’t help but think how grateful I am to share this desert canyon with these remarkable animals. Although they may have a fearsome reputation among some folks in this region, I’ve never had anything but congenial interactions with rattlesnakes, and have, in fact, come to regard them as perhaps one of the kindest and most thoughtful of snakes.
Where else, but here in the Americas (the only place in the world where rattlesnakes evolved), do venomous snakes offer such an obvious warning of their presence? In my experience, they really don’t want to have to bite you and try to give you every chance to reconsider your life choices before they lash out. Sure, some, such as the Mojave rattlesnake have a reputation for aggression, but even if true (though apparently the scientific literature does not support the idea that Mojaves are especially aggressive), it seems that this apparent “aggression” is more of a case of “the best defense being a good offence”.
With their potent venom and specialized fangs, heat sensing pit organs on their faces, and the distinctive rattle that forms at the end of their tail, rattlesnakes may just be the most specialized and unique group of snakes in the world.
The rattlesnakes in our region eat a variety of prey including small mammals, lizards, birds, other snakes, and invertebrates, and their venom can quickly immobilize most of these other animals. Their venom is a cocktail of chemicals; enzymes, peptides, minerals, and other substances that together have hemotoxic (blood and tissue disrupting), and sometimes neurotoxic (nervous system disrupting), effects, and can also begin the digestion process in the body of the envenomated animal [i]. Amazingly, some prey species have evolved immunity or resistance to rattlesnake venom, including woodrats and rock squirrels [ii],[iii].
Their pit organs are another adaptation that helps rattlesnakes in the hunt for food. These organs sense heat in the surroundings and the input from them is combined with visual input in the snake’s brain to create a heat-vision sense which can allow rattlesnakes to accurately strike prey, even in total dark [iv],[v].
As opposed to their venom and pit organs, rattlesnake’s rattles have evolved purely for defensive purposes as a warning mechanism for potential rattlesnake predators. The rattle is formed from keratin scales at the end of the tail and a new segment is added each time a rattlesnake sheds it’s skin. Depending on how much they are eating, shedding can happen multiple times a year. For this reason, and because the rattle segments regularly break off, it is not possible to determine an adult rattlesnake’s age by the number of rattle segments.
Here in the Sky Islands we are especially lucky to have 10 rattlesnake species living amongst us, with at least another 4 living just outside our region in other areas of Arizona and Sonora [vi],[vii]. Arizona, with 13, has more rattlesnake species than any other state in the U.S., and some, such as the twin-spotted and tiger rattlesnakes, are found nowhere else north of Mexico.
I’ve been frozen in place for nearly a minute, hoping that the rattlesnake at my feet will have moved on, but not able to see or hear if it has done so. As I slowly raise my foot, it’s loud rattle once again breaks the night’s silence: it doesn’t seem to have moved at all. Not wanting to provoke an attack, I once again fall still, hoping that this time the snake will be motivated to get on its way.
When another attempt to raise my foot a few moments later is answered by yet another long buzz, I decide that perhaps it’s time to risk a slow retreat. I back away with the ever-present noise of the rattle accompanying my steps, and as I move into the rocks to the side of the trail, I can finally hear that the snake is on the move.
Very slowly and cautiously, I take a route off to the side of the trail, while the rattlesnake does the same opposite me. We circle one another for a moment while I silently extend my gratitude for not being bitten as I backed away. Soon I’m back on the trail and once again gingerly making my way towards home. This will not be a night I soon forget…
Sources
[i] Cetaruk, Edward W. (2005). “Rattlesnakes and Other Crotalids”. In Brent, Jeffrey (ed.). Critical care toxicology: diagnosis and management of the critically poisoned patient. Elsevier Health Sciences. p. 1075.
[ii] Perez, John C.; Haws, Wills C.; Hatch, Curtis H. (May 1977). ”Resistance of Woodrats (Neotoma micropus) to Crotalus atrox Venom”. Toxicon. 16: 198-200.
[iii] Holding, Matthew L.; Drabeck, Danielle H.; Jansa, Sharon A.; Gibbs, H. Lisle. (November 2016). ”Venom Resistance as a Model for Understanding the Molecular Basis of Complex Coevolutionary Adaptations”. Integrative and Comparative Biology. 56(5): 1032-1043.
[iv] Newman, Eric A.; Hartline, Peter H. (March 1982). “The Infrared “Vision” of Snakes”. Scientific American. 246 (3): 116–127.
[v] Ivanyi, Craig. (2000). Rattlesnakes. Arizona-Sonora Desert Museum. Retrieved from https://www.desertmuseum.org/books/nhsd_rattlesnakes.php. June 12, 2020.
[vi] Brennan, Thomas C.; Holycross, Andrew T. (2009). A field Guide to Amphibians and Reptiles in Arizona. Arizona Game and Fish Department. pp. 124-133. ISBN 0-917563-53-0.
[vii] Rorabaugh, James C. (2008). ”An Introduction to the Herpetofauna of Mainland Sonora, Mexico, with Comments on Conservation and Management”. Journal of the Arizona-Nevada Acadamy of Science. 40(1): 20-65.