Friday, May 7, 2010

Rare encounter: A Mojave Rattler

We live in the Bajada of the west side of the Tucson Mountains. Yesterday morning my husband Randy, our dog Cody, and I went to the eastern part of our property to check out the blooming chollas. A Desert Iguana Dipsosaurus dorsalis was bobbing his head in a territorial display. They aren't very common here and I'd found one of them dead this spring, so we were very happy to see this one.

Then the short dry grass right behind the big lizard moved and a snake slithered by, not two feet from him. The very straight movement identified it as a rattler, other snakes move in a more undulating manner. Where lacy Creosote shadows and its own markings made it nearly invisible, it flattened itself to the ground. Snakes, who have no sternum, actually spread their ribs to do so. This pose allows them to absorb a maximum amount of heat from the warm sand and from the radiation of the sun. It eliminates most of the cast shadow which hides the snake even better.
This snake turned out to be a female Mojave Rattler, Crotalus scutulatus. Thanks, Brendan O'Connor, for verifying my identification which was based only on the wide white /narrow dark bands of the tail. More reliable diagnostic markers are the facial scales and the band that runs from the eyes to the corners of the mouth. I didn't want to get close enough to record those with my 50 mm Macro lens.

We left the rattler alone - with trepidations. Rattlesnake venom is mostly haemotoxic, extremely painful but rarely deadly to larger animals and humans. But with squirrels becoming more and more immune to it, Mojave Rattlers co-evolved by producing a neurotoxic venom component known as Mojave Type A toxin- which puts them in the same class as the deadly Cobras.
This snake had a very small rattle for her 2.5 foot body length. A rattler adds a section to its rattle each time it sheds its skin which happens several times per year. This one must have broken off parts of it. She also never bothered to rattle even though I was very close.

Cody was strolling around but never noticed her. He is snake trained (the hard way) and he flinches even from black and white ribbons, curved branches, or the smell of my snake stick. Occasionally he's fooled by a Gopher Snake. He has a clearly recognizable, rhythmic 'snake bark' that will alert me from my deepest dreams. Rolling out of bed, grabbing some shoes, the snake stick and a flash light, then locating and holding the snake until Randy arrives with a container, has become the routine of hot summer nights when the snakes seem to follow the walls of our house right to the patio and the dog beds. The following morning we carry the captive out to the adjacent State Land for photo shoot and release. From May to September last year we had to move 14 Diamondbacks from patio and dog-run. Elsewhere on our property we leave the snakes alone and appreciate them with the rest of 'our' wildlife.
Western Diamondbacked Rattler
Crotalus atrox


  1. Woah, that western DB photo is great. It reminds me of one I took recently of a prairie rattlesnake in the Black Hills of South Dakota (see my post Rattled in the Black Hills).

  2. Great writeup. I am glad you included the details of Mohave identification. The tail bands are highly variable. People often report seeing Mohave Rattlesnakes in Sabino Canyon. According to David Lazaroff, there has never been a confirmed siting there. You might be interested in seeing my slideshow of a Common Kingsnake eating a Gopher Snake. Go to and scroll down near the bottom of the home page. I hope to see you up on the Mountain on Wednesdays this summer with Ned and Jean.

  3. Manny Rubio, author of 'Rattlesnake - Portrait of a Predator' emailed in answer to this blog 'That is definitely a Mojave, and the closest to my house that I've seen. The nearly 100 rattlesnakes that I've seen in the neighborhood have all been Western Diamondbacks and one Black-tailed Rattlesnake.'

  4. I take back my comment concerning David Lazaroff. In his book he says "it is likely that individual Mohave rattlesnakes occasionally reach the Recreation area or did so before urbanization decimated the local population."

  5. Interesting story and details! I saw a Mojave Rattler on my trip last month in Kern County, under a creosote bush at my campsite. It was the only warm evening on my whole trip and I'd wanted to put the bug light up... but ended up not doing it because the snake wouldn't leave and messed up my plans.

    Anyway, later a colleague at UC Berkeley confirmed the id of the snake from photos. Turned out she'd been in the Mojave looking for this species at the same time and hadn't found any. So I felt I'd seen something special and forgave it for messing up my one warm evening!

    My Mojave Rattler rattled quite a lot -- pretty much nonstop if we walked in the campground. So it was hard to miss it. Interesting that yours was so quiet.

    I wish we'd had someone with us who knew how to safely move the snake... The snake eventually left but by then I had to go to sleep.

  6. Hi Joyce
    I had to move Diamond-backs twice from my bug light last summer. First came the bugs, then the toads, then the snakes...the whole feeding chain. I have made two kinds of snake sticks, hooks and a noose. The noose is harder on the snake I was told - they always look just fine after the ordeal. The hooks work safely in open areas with no interfering brush. I think I'll get one of the professional grasping sticks this year. Removing is easy - stay more than out of reach, they can lunge two thirds of their length - stay very calm - have a deep container with a well fitting lid, a pillowcase works, too - and always, even in the early morning, keep the captive snake out of the sun. Releasing it close to where you found it is always best.

  7. Our state herpetologist has been doing an on-going study of rattlesnakes in Missouri (mostly timber rattlesnakes). During the course of this 13+ years study he has determined that rattlesnakes are rattling less and less. He has many of them radio tagged and walks right up on them and they do not rattle.

    We own a farm in the river bluffs of NW Missouri, there are numerous timber rattlesnakes on this farm. Last summer I went there with the purpose of photographing rattlers. I walked by a tree that had a pile of limestone rocks near it. I felt pretty sure that would be an ideal spot to locate a basking snake. After not spotting anything I walked on, only to have my husband tell me that there was indeed a rattlesnake by that tree. I went back to see what he was pointing at and sure enough there was a 2 foot long timber rattlesnake hidden in the grasses. At no time did this snake rattle, even when we located a sturdy stick to try and coax it's head out of the grasses for a photo, still it remained silent. The opinion around Missouri is that the rattlesnakes are evolving to a more silent nature to keep from being killed by fearful humans. The rattle that once protected them on the plains from being stepped on by large hoofed animals is now a calling card to death. I know so many people who admit to killing them out of fear. Seems it is in the snakes best interest to keep quiet. The Mojave rattlesnake that you photographed is simply gorgeous, thank you for sharing the photo and story behind it.

  8. Research has shown that Rattlers (as any other organism) are adapting to changing environments. Mojaves for example are increasing the neurotoxic component of their venom in response to higher toxin resistance in squirrels. It's also becoming obvious (Texas A&M studies)that this adaptation speeds up when a lot of big, old snakes in an area are regularly killed as it happens in many places in Texas where mass snake killings are organized public events. The killing of old territorial snakes leads to shorter generation sequences, younger populations and faster adaptations. Your example sounds even more straight forward than the Texan case because the assumed adaptive change would be a direct response to human 'predation' pressure.