Monday, July 27, 2015

Bryan Hughes Tackles a Western Rattlesnake Mystery from Arizona

Hi Dr. Steen-

    I saw the Slate article about your website awhile ago and so when my husband and I found a few snakes around our house recently, I thought I'd send the pictures along. The first photo is of what I think is a Western Diamondback. It had the black and white stripe pattern above the rattles on the tail, but didn't seem to have to greenish tinge that the Internet mentioned of the Mojave rattlesnake. It was curled up right against the gate going into the backyard. My husband and dog might have walked right past it on the way out of the yard but my husband noticed it on the way back in. The dog has had snake training in the past but he didn't appear to notice the snake at all. 

    I didn't want to have to kill it so we used some gardening tools and hose to spray it away from the backyard. It was very angry-lots of rattling, but found a bush to crawl under a short distance away and I haven't seen it since. Any way to know if it was male or female? We live on the edge of Tucson, Arizona right up against Tucson Mountain Park-West, so we see all kinds of animals all the time. Javelinas, coyotes, bobcats, deer, great horned owl, roadrunners, scorpions, centipedes. A month or so ago we had a gila monster in the front yard.

    Anyways, the next picture is from this last week. The dog and I went out about midnight and found these 2 snakes knotted up under a rock. I put the dog away and went out for some pictures. The black striped one (a small king snake?) had the other snake's head in it's mouth. I couldn't figure out how the black snake was going to eat the other one since they seemed about the same size. I went to bed, got up on Wed. and both snakes were gone. Then, Thursday morning my dog was sniffing around and we found the lighter colored snake dead, apparently it hadn't been eaten. Unless it was a different snake completely. It had a body wound and was in a different part of the yard than when I had seen it Tuesday night. So I don't really know what happened. Was it too big to eat? Was the wound from being constricted by the other snake? 

   My husband took this picture of the dead one with the quarter to give a sense of scale. I don't have any idea what kind of snake the dead one was either, probably something harmless. 

    Thanks for all your help and have a great weekend!

Elizabeth A.
Tuscon Arizona

    What an incredible series of observations! I wanted someone more familiar with western species to tackle Elizabeth's interesting questions so I contacted Bryan Hughes. 

    Bryan Hughes is an avid herper and photographer in Arizona, field researcher, and a regular speaker at regional parks and reptile-related events in Arizona. His work can be seen on twitter (@rattlesnakeguy), and fieldherper.com, a photography-focused journal of snakes. He is also the owner/operator of a Rattlesnake Solutions, a rattlesnake-focused conservation and education business in Arizona. Here is his response:

Elizabeth,

    It sounds like you have an amazing yard! Many of us snake-nerds dream of a scenario where we could see a gila monster hanging out in the front yard. 

    You’re correct in your identification of the Western Diamondback Rattlesnake, Crotalus atrox, that you found in your yard. The tail-banding is one way to differentiate them from Mojave Rattlesnakes, Crotalus scutulatus, but that can get muddy in some parts of the Mojave’s range, where tail banding can look somewhat similar. Generally (as you may have read), the tail banding of a Western Diamondback is about 1:1 ratio of white to black, while the Mojave is more in the neighborhood of 2:1 white to black.

    Diamondbacks can be wonderfully variable in color, pattern, and size. They don’t tend to show much in the way of green coloration, however, especially in the Western end of their range. Mojaves also aren't green through much of their range. They certainly can be in some areas, like around Lake Havasu, or in the valleys East of you, near Elgin. In your area, most that I have seen are straw-colored or tan. 

    Something else you can use to differentiate between a Diamondback and a Mojave is the pattern. While the pattern of a Diamondback and a Mojave are superficially similar, the diamondback generally has a much more speckled, “dirty” appearance, as in the photo that you sent in. The diamonds (especially on older animals) tend to break apart and have varying degrees of black splotches or broken white outlines. A Mojave rattlesnake, in contrast, has a much more clean pattern with very little to no speckling. Most scales are generally one color.

    The area where you live is also a factor. Mojave rattlesnakes do live in the area. However, once you get into the rocky bajadas and hills along the side of the mountain, the likelihood of seeing a Mojave drop off dramatically. They much prefer the sandy, flat areas several miles to your West.

    It’s difficult to say whether your Diamondback is a male or female, without seeing more of the body and tail. Females generally have a body that remains wide until just before a short tail, with a short taper just before (or sometimes right at) the  start of the tail banding. Males have a much more gradual taper throughout the latter half of the body, which ends in a longer tail. With diamondbacks, the stripes make it easier to specify just how long is a tail on an animal that seems to be all tail. Generally (this could differ depending on where you are), in your area, fewer than 4 black bands will be a female, and 4 or more bands is a male. If I were to take a gut-guess based on body proportions and head-shape alone, after seeing thousands of them, I would say that your snake is a female. Of course, take that with a big grain of salt, and send in a photo of the tail if you happen to see her/him again.

    The two snakes in the second photo are, as you guessed, a young Desert Kingsnake, Lampropeltis splendida, and a Desert Nightsnake, Hypsiglena chlorophaea. Kingsnakes eat other snakes, and nightsnakes are on the menu. They can eat snakes that are up to about the same body size as they are, amazingly, so I have no doubt that this kingsnake finished its meal and went off to digest it somewhere. Also as you guessed, both are harmless.

    I would assume that the third snake, which is also a Desert Nightsnake, is a different snake that died of other causes. Life is tough this time of year and it’s not at all uncommon to find snakes that haven’t made it through the fore-summer for one reason or another. This one looks to be dried up and shows some wear and tear in the scales that wouldn’t be likely in the timeframe mentioned. 

    Thank you for sharing, and for your positive attitude with wildlife on your property. As someone that often deals with the other side of how these encounters often go, it’s refreshing to see and I very much appreciate it. 

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