Friday, December 19, 2008

Snake Skin


Finding a snake skin is almost as exciting as finding the actual snake. To me anyway. I've found them in open fields, along fence rows, around the bases of trees and many other places. Similar to animal tracks and other sign, finding a snake skin in the field can help you determine the types of snakes in your area. The one in the photo was found in October on the sandy floor of our barn. The crinkly, cellophane-like remnant lay stretched out next to an old gate I had stored there. The snake probably used the rough surface of the fencing on the gate to help in the process of shedding this perfectly sloughed skin. I looked it over carefully and could not find a tear or defect anywhere. It was entirely intact, an exact representation or replica of its owner. There are several factors that affect the frequency of shedding or “ecdysis”, but basically younger snakes shed more often (as much as 3-5 times a year) due to growth and adults shed less often (1-2 times a year) due to a slowing growth rate. During the process the scales of the snake become dull and the eyes become opaque to the point that the snake’s vision is impaired. This makes the snake skittish and extremely defensive because it can’t see as well. I experienced this behavior with a shedding diamond-backed water snake I came across while hiking with my brother and his son. You may have read about this in a prior blog entry. This particular snake already has a nasty disposition so you can imagine how aggressive its behavior is when it can’t see. Once the snake is ready to detach itself from the old skin it finds a rough surface and begins to rub the area around its nose and mouth until the skin comes loose and begins to peel back. It will then crawl through or up against a rough surface enabling it to slide right out of it like a glove. It’s a slow and deliberate process that sometimes takes several hours. Now the question that beckoned was- what type of snake left this behind? I took it back to the house and began to examine it closer in order to help me determine this. Since coloration and markings are lacking on the shed skin I had to rely on other aspects.

The first thing I noticed was the fact that the scales were smooth and not keeled. Smooth scales reflect light which makes snakes with these types of scales very glossy in appearance. Keeled scales on the other hand have a ridge running down their center and reflect less light giving snakes with this type a dull, rough appearance (a plus because it provides more effective camouflage). Next, I checked out the condition of the anal plate. Snakes have an anal plate that is either undivided (single) or divided (double) and I found that this one was divided. I then counted the dorsal scale rows at mid-body and found it to be 17 scales.

Finally, and the most important feature I examined, were the head scale or plate characteristics (type, number, shape, and arrangement) of the dorsal (top), lateral (side), and ventral (chin area) plates.

By comparing these plates with sketches (along with the other criteria mentioned above) I found the owner of the skin to be an eastern coachwhip (Masticophus flagellum flagellum). This was really not surprising to me since they’re prevalent in this area and also due to the fact that I've caught several.


As with most things in nature nothing goes to waste- not even a snake's shed skin. Great-crested flycatchers, Carolina wrens, and the tufted titmouse all collect discovered snake skins and incorporate them into their nests. It's not really understood why they do this, but there is a theory that the presence of a snake skin in the nest will ward off predators. Recently I came across an article on the Science Daily website that explained how California ground squirrels and rock squirrels will take snake skins, chew them up, and then rub them onto their fur in order to hide their scent from predators.

One caveat must be mentioned about the handling of snake skins. The fact that they can harbor Salmonella. "Researchers in one university laboratory found viable Salmonella organisms on skin sheds that had been hanging in their lab for years." Be sure and wash your hands thoroughly after handling them.

Sources:

University of California - Davis (2007, December 25). Squirrels Use Old Snake Skins To Mask Their Scent From Predators. ScienceDaily.

http://www.anapsid.org/shedding.html

http://www.sciencedaily.com/releases/2007/12/071219130305.htm

http://newton.dep.anl.gov/natbltn/100-199/nb179.htm





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4 Comments:

Blogger Pam Croom said...

Wow, great photos. How long was the skin?

Very nice write up on keying out a snake by the skin.
Very nice blog.

7:51 PM  
Blogger Jace Stansbury said...

It was exactly 5 feet in length. Appreciate the compliments!

Jace

8:17 PM  
Anonymous Neil said...

Wow that is a pretty complete skin - ive only ever come across bits of them here in the UK

7:11 PM  
Blogger Jace Stansbury said...

Neil,

I've been fortunate to find several complete skins. Thanks for reading.

Jace

7:26 PM  

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