Southwestern Field Herpetology

Southwestern Field Herpetology

Sandy Situations: Convergent Evolution for Life in the Desert

This post is part of #CrawliesConverge, a series of posts highlighting convergent evolution in reptiles and amphibians. More at RAMBIN, and on twitter.

In Arizona, we have a little desert rattlesnake that everyone has heard of, but not many people seem to know much about or have actually seen … or even know that we have them here. It’s the sidewinder (Crotalus cerastes), one of my favorite little rattlesnakes to find out here, and master of desert specialization.

They get the name in the same way that a lot of snakes get their names: bluntly labeled for something that they do. To move quickly over the hot sandy soil, they have evolved a particularly iconic behavior: sideways scooting over the sand by throwing a loop of their body forward, then pulling the rest alongside. This not only makes them the fastest rattlesnake1, but one that is able to move over hot ground that would otherwise kill it. They’re very common wherever they range, and are quite easy to find with just a little bit of effort – when you see one, it gives its identity away by the way it moves.

So, why do I hear at any education event where I’ve brought one to, “a sidewinder is a rattlesnake?! Wha!”? Everyone’s heard of a sidewinder, but a smaller portion of us know that they are a rattlesnake, or that they live here. They’re not at all misinformed. On the other side of the world, there is also a sidewinder that looks and acts very similar to our own little rattle-tailed variety.

It’s the Horned Viper (Cerastes cerastes), and it’s not even closely related to our sidewinder in the US. The split occurs up at the family level. Which means, as far as taxonomic categorization is concerned, they are as different as dogs and cats. They’re found in the middle east and parts of Northern Africa … a world away, so how similar could they possibly be? Here they are, side-by-side:

There’s more, too, than just movement. In pattern, these animals are remarkably similar.

Horned Viper:

Mojave Sidewinder


There’s more, too. Above each eye is a scale that has adapted to be a horn. It’s not exactly known why these exist; their function has several theories attached. One of which is that they could be flexible, or otherwise protect the eyes from blowing sand2. Regardless of cause, both of these snakes have evolved a similar structure to solve what is most likely a similar solution.

Horned Viper:
"Hornviper Cerastes cerastes" by H. Krisp - Own work. Licensed under CC BY 3.0 via Wikimedia Commons -

Sonoran Sidewinder:
Crotalus cerastes cercobombus


This similarity between animals on opposite ends of the Earth is one of my favorite, go-to examples of convergent evolution; perhaps because it comes up so often in day-to-day talking to people who are curious about snakes. Completely independently, they’ve found very similar solutions to common problems. If animal life on Earth were ‘rebooted’ and these snakes never existed, it’s extremely likely that snake-like animals would end up in similar places, where sand forces evolution to provide answers to life in challenging conditions. By procedure alone, the answer to how to live in the hot sand, if you’re a snake, is to look, act, and move like this.

Now, time to quit typing and get out to my favorite sidewinder-viewing spot before the sun sets! Check out the rest of the #CrawliesConverge posts on twitter.


2. Cohen A. C. & Meyers, B. C. 1970. A function of the horn in the sidewinder rattlesnake Crotalus cerastes, with comments on other horned snakes. Copeia 3, 574-5.


Arizona Glossy Snake from the Phoenix Area

Arizona Glossy Snake, Arizona elegans noctivaga



Speckled Rattlesnake from the White Tank Mountains

We saw this cool speck in a dark hole in the White Tank mountains, West of Phoenix. “Cool” is a relative term, which describes what this animal was trying to do on this particularly blazing day at the peak of summer hot and dry, like only Arizona knows how to do.




My Favorite Observation of 2014 – Crotalus lutosus Combat with my Leg

In the Spring I spent about a week at some C. lutosus den sites up North. I spent a couple of those days more or less standing in place for hours at a time, finding alternative uses for a snake hook (which is pretty much just a hiking stick at this point) as something to lean on.

Why was I standing there? I wanted to get combat photos. This den is a pretty big complex, with each group seeming to have one big male, several females, and a few other males hanging around. At one particular point, there were more, larger males, and females that moved between the smaller zones quite a bit. I figured this would be a good spot to find some conflict that would be more than just a big snake chasing a little one off. So I spent a lot of time just watching everything they did, standing more or less right in the group of rocks where they were, as still as possible. It’s actually kind of amazing how entertaining staring at a stationary pile of snakes is if you’re interested.

Anyway, I saw a lot of cool things that week, took a lot of photos, and I did get some combat (and video), and more. The best part to me, was when the big male in this zone chased a similar-sized one to rocks just below my feet. The defeated snake took off (I saw him later in another area 20′ or so away). The victor went to court his pile of females. In the middle of this, I had to shift my weight, and was spotted by him. He came out at me with his head raised, attempting combat with my leg.

I moved my hiking stick out front in case there was contact (I didn’t touch him of course), but there was none. He would stand up and do his thing around the rocks at my feet. When it got to where he actually flopped down ONTO one of my boots that I decided to step back (after he’d slid off). As soon as I left, he went right over to court with the females.

In the next few days, I could reinitiate this behavior with him any time by approaching and standing in that spot, and moving gently moving grass near his rock. More amazingly, I reproduced this with another group days later (to a lesser degree, but I was retreating much sooner). I was able to show this second instance to Kris Haas, who’d flown up to join me at this point.

To anyone worrying that I’ve interacted with a group in such a sensitive situation – this wasn’t my intention. I’ve already been watching this group for a few days at this point, so I didn’t miss the in situ observations that could be disrupted by my being there. I also was never buzzed or even tongue flicked. I take great care to not disturb anything.

Here are some photos, which were hard to get since this was happening right below me, and I had a 100mm prime on. Once he got closer, I couldn’t get anything at all.






Red Diamond Rattlesnake – Up Close



Eastern American Toad – Anaxyrus americanus americanus

Right after getting into PA for the first time, this is my first Eastern herp. Just a little toad, but a new one, and everyone had to endure me taking too many photos of it before we got to our first timber rattlesnakes a half hour later.



Pair of Western Diamondbacks from Ahwatukee (South Phoenix)

These were relocated from the neighborhood below. This is a big part of why I love Phoenix, and where most of the gas money for my herping trips comes from.

Western Diamondback Rattlesnakes


Beautiful Great Basin Gophersnake from the Southern Range of the Subspecies

Seriously … look at this thing. I wonder how it would look as an adult. This is probably the prettiest gophersnake I’ve ever seen, found in Arizona near the Southern border of their range.



Arizona Ridge-Nosed Rattlesnake in Ambush

Camo doesn’t work as well when against a burnt-out tree. This snake may not succeed in the day’s hunt, but I don’t mind today.

Crotalus willardi


Lone Timber Rattlesnake at Spring Basking Site

Timber Rattlesnake


Sonoran Mud Turtle Underwater

Moving through the water, undisturbed, hunting for invasive crawfish and poking through the mud, this little mud turtle made my day.



Timber Rattlesnake Accidents

Well, not quite, but barely! See the pile of black timber rattlesnakes? That’s what I saw too.

timber rattlesnake den

What I didn’t see was the big yellow-phase timber right where I just about put my hand! Yikes. I saw him just before it was too late.



Yes, that would have hurt.

And, here’s a closer shot of the black timbers, minus 2 that disappeared before I could get a shot.