Wednesday, August 22, 2012

Readers Write In: What Is This Snake? The Remix

There is a serpent marauding through the backyards of Greenville, Kentucky and the people of this town need our help to identify the creature.

"Dr. Steen,

...I found your site because I have been searching the internet for images of a snake we recently found in our backyard.  I live in western Kentucky.  A few mornings ago I went to fill up one of my birdfeeders and there it was.  It was about four feet long.  I've actually seen very few snakes in the wild and this was certainly the first that i've seen in our yard.  I am hoping it was a (deleted to maintain suspense) and about 50% of the people I've polled agree BUT the other half say they are not so sure. One person even mentioned a boa or a python...I haven't found any images that look exactly like the photos I took of it. The colors are certainly similar to a (more suspense), size matches up to what I've read, and they are in this area, however, the yellowish spots on its back go down its back vs across.  Are you able to help me ID this snake so I can stop freaking out over it?

Lynette L.
Greenville, KY"

In a follow-up e-mail, Lynette mentioned:

"Thank you again for your help.  It was very frustrating looking for pictures online that looked like my snake's markings.  If possible, could you perhaps address that point in your post. I left it alone and it slithered into my ivy.  Needless to say, I won't be gardening around that spot any time soon.  It was creepy but I respect that it serves an important part in nature."

Lynette touches upon a common frustration: it is often difficult to determine what species a snake is just by looking at pictures. When people encounter a snake, they often focus on certain features that are not useful for differentiating between species. For example, people will sometimes tell me that a snake they saw had yellow stripes or brown blotches. These stripes or blotches may seem distinctive to them but there are often many different species that share the same characteristics. In addition, even snakes that are the same species can look very different.

That's why the most reliable and accurate way to identify species is by using a dichotomous key (a good one, at least). A dichotomous key is basically a series of questions about the organism you're trying to identify. Here's a hypothetical example:

1. What color is your snake?
A. Blue...go to #2.
B. Red...go to #3.

2. Does your snake breathe fire out of its nose?
A. Yes...It's a Fire Serpent.
B. No...It's a Smokesnake.

3. Does your snake smell like pizza?
A. Yes...It's a Pepperonisnake.
B. No...It's a Waffleviper.

There are other, similar ways to identify snakes, like this series of questions developed by the Herpetology Lab at Davidson College. 

Most of the time I can just look at a snake and know the species but sometimes I have trouble differentiating between snakes that are closely related, in these cases my preferred method is to use Peterson's Guide to Amphibians and Reptiles (there is a link to this book on the sidebar) because this book makes it very clear which subtle differences I should look for when I'm trying to tell apart very similar species.

Lynette's question is timely. Last week I attended a herpetological conference in Vancouver, British Columbia, and saw a presentation by Living Alongside Wildlife contributor and frequent commenter Andrew Durso about this very topic. He notes that snake experts often tell laypeople to pay attention to very specific features and characteristics to figure out, step by step, which species of snake they are looking at. However, when these snake experts identify a snake themselves, they rarely have to rely on these features, they can just look at a snake and know the species, based on the overall look of the animal (except for those rare cases when two species are very closely related). For example, when I looked at the pictures of the snake we are being asked to identify, I didn't examine the shape or size of the animal, I didn't look at the patterning or at the patterns of scaling. I just looked at the picture, took the feel of the animal in, and knew what it was. I hope Andrew elaborates on this inconsistency below.

But, back to the original question. What is this snake? I expect many of you already know but please chime in and let us know the last time you saw one of these animals. In addition, if you have thoughts on how people should identify snakes, let us know those as well.

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