Friday, January 13, 2012

Readers Write In: Grey Ghost Rattlesnakes in Wyoming?

A reader recently wrote to me in the hopes of shedding some light on a rattlesnake mystery from northern Wyoming. The original e-mail is below (I have edited for length and clarity).

I was involved in a rescue event in late August in N. Wyoming.  For reasons too complex to go into here I found myself in knee-to-waist high mesquite brush in pitch-black darkness, wearing nothing but shorts, personal flotation, and kayaking slippers.  I was using an LED light, which produced a bluish beam.  I came upon three rattlesnakes within a radius of less than 100 feet.  Two were actually within about ten steps of each other.  They were the palest shade of grey I had ever seen in a snake -- almost white, void of markings.  They were the absolute exact same color as the ground.  My bluish light was probably producing some color distortion, but if so, it was distorting the color of the snakes and the ground in the same way.  

A small rattlesnake (Pigmy Rattlesnake) from Florida
At the time I saw the first snake I had been climbing around in the bush for an hour, and I freaked out.  I was being fairly vigilant but not really expecting to see rattlers in those conditions (or at that elevation). These snakes were not large.  Although it hard to guesstimate the length of a coiled rattler, I would say less than 18".  Their camouflage was so perfect that they were nearly impossible to pick out.   Although I could see their rattles, I couldn't hear them because of the high wind. 

Any guesses as to the species?  Any thoughts as to why I would have stepped by three of these things in such a small area?

Denis O.

There are a number of serpentine mysteries to unravel here. First off, what species of rattlesnake could this be? Although Wyoming is not the first place many people think of when asked to imagine a good place to find rattlesnakes, there are two species native to the state: the Prairie Rattlesnake, Crotalus viridis, and the Midget Faded Rattlesnake, Crotalus oreganus. In Wyoming, the Midget Faded Rattlesnake is only found in desert habitats in the southwestern corner of the state. We can safely conclude that the species the reader observed was the Prairie Rattlesnake.

Prairie Rattlesnakes, along with several other species of rattlesnakes that live in high latitudes or elevations, may be found in large numbers near den sites. I suspect that the reader was trudging through an area close to a den site, which explains why he would find three in a relatively small area (usually rattlesnakes are found few and far between, especially in the southeastern United States where they do not typically den together).

It is difficult to estimate the size of coiled rattlesnakes
(here, another Pigmy Rattlesnake)
Let’s move on to the lengths of the snakes. Eighteen inches (about 46 cm) is not a very large rattlesnake. Considering it is human nature to overestimate the size of rattlesnakes (as well as the reader's admission that it was difficult to determine), let’s assume that the snakes were slightly smaller. This is about the right size for neonate (that is to say, newborn) rattlesnakes, which tend to be born in late summer or early fall. Since the snakes were observed in late-August, this explanation makes sense.

The apparent color of the snakes is interesting. The reader reported them as grey, almost white. Although there are albino rattlesnakes, it would be very unusual to find three in a lifetime, let alone in one night. I think the appearance of the small snakes can be explained with a combination of rattlesnake biology and the choice of flashlight.

Newborn rattlesnakes don’t tend to move far or do much until they shed their skin for the first time, which often happens within their first few weeks. Before a snake sheds their skin, the old skin may appear gray. This appearance was probably heightened by the use of an LED light. I have overheard many debates among herpetologists regarding the use of LED vs. more traditional halogen bulbs. Although LED lights are brighter, they produce a light that is less “natural”. When looking for reptiles at night, I prefer LED lights because they illuminate a larger area. However, they may wash out colors. It is easy to imagine how a snake that is about to shed their old and gray skin might appear even more gray when lit up by an LED.

Finally, because rattlesnakes develop their rattles by adding new segments after each shed skin, a newborn rattlesnake would not have a functioning rattle. This explains why the reader did not hear their telltale warning signs. Although newborn rattlesnakes might not be more dangerous than adults, their venom does pack a punch. This is a good reminder not to handle a snake just because it doesn't sound (or look) like there is a rattle.

So, in conclusion, the most likely explanation for this observation is that the reader stumbled onto a Prairie Rattlesnake den and several newborn babies. That the babies had not yet shed their skin, as well as the use of an LED light, explains why they appeared gray and did not produce any rattling noises when disturbed.

Thanks for writing in with your questions. Keep them coming.


Most of what I write is based on my experience in the field, however, I also rely on the research of others. Here's a relevant article:

HOLYCROSS, A., & FAWCETT, J. (2002). Observations on Neonatal Aggregations and Associated Behaviors in the Prairie Rattlesnake, Crotalus viridis viridis The American Midland Naturalist, 148 (1), 181-184 DOI: 10.1674/0003-0031(2002)148[0181:OONAAA]2.0.CO;2

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