Tuesday, April 21, 2009

A Case of Mistaken Identity Part I

     A few years ago I was up to my waist in muddy water, helping lead a class of undergraduate students through the murky depths of Chickasawhatchee Swamp to expose them to some of the unique ecosystems of southwest Georgia. It wasn’t long before a student straggling behind the group excitedly shouted that he had found a cottonmouth. Excited and with adrenaline pumping, I trudged through the water to a small patch of land where he was enthusiastically pointing to a snake coiled around some grass and partially concealed by an old stump. While splashing noises behind me signaled the arrival of the rest of the class, I quickly realized the snake in question was not actually a cottonmouth but a large plain-bellied water snake (I have found that almost without exception, a person not particularly familiar with reptiles will identify any snake they find as a venomous species).
 I wanted to catch the water snake to show the students, but being an ornery species it did not take well to the harassment and tagged me several times before I had it firmly and safely within my grasp. With my blood dripping down my hands and into the water around me, I turned around and presented the four foot long snake to the group with a huge smile. As I looked at their horrified expressions and open mouths, it dawned on me that I hadn’t made clear to them that the initial identification was a mistake. I hurriedly corrected my oversight and informed that I had not, in fact, been bitten multiple times by a cottonmouth, but instead by a harmless water snake. They were visibly relieved.
 Before we examine how to accurately differentiate between venomous cottonmouths and non-venomous water snakes, let’s first address their names. A cottonmouth’s scientific name, (Agkistrodon piscivorous) cannot be mistaken with anything else, but there aren’t rules regarding what other names it can be called. For example, cottonmouths are often referred to as water moccasins. It’s not entirely accurate to call other snakes moccasins, but many do. Much confusion can be averted by using the word moccasin only when speaking of the venomous cottonmouth.
 It’s difficult to describe how to identify a snake. A picture tells a thousand words. Some of the characteristics I describe below may be subtle, and it may take some time looking at actual snakes before you can easily identifying them and notice their unique features. But that’s the most effective way of becoming comfortable identifying snakes, looking at a lot of them.
 Much has been said about how venomous pit vipers can be distinguished from non-venomous snakes by their triangular-shaped head.
Note the head shape on this venomous cottonmouth
     It’s true that this shape can be used to differentiate them, but many people have pointed out to me that sometimes, if you look hard enough, even harmless snakes can appear to have a triangular shaped head. I’ve seen many non-venomous snakes that may flatten out their head when they’re threatened, making a distinctive triangular shape. Most people haven’t looked closely at many snakes, therefore when one suddenly appears there’s not much to compare it to. For this reason, I don’t often put much stock in using head shape to identify snakes.
Note the head shape on this non-venomous ratsnake
     Cottonmouths have very thick bodies and they’re often covered by dark bands. However, examining a snake’s patterning is not always a useful way of identifying snakes, different individuals often have varying degrees of patterning, and older snakes may become mostly dark over time.

     I don’t advise you to get too close to a snake unless can you identify it, but another way to differentiate a cottonmouth from non-venomous snakes is by the shape of its pupil. Pit vipers have vertically oriented slits; other water snakes have round pupils.
   One unique feature of cottonmouths (and closely related copperheads) is that young snakes have a bright green or yellow tail (they lose this color as they age). It’s thought that by wriggling their bright tail, cottonmouths can lure in curious lizards, which are promptly eaten.
    The venomous cottonmouth, which is a pit viper (like rattlesnakes), can be very common in our area; in some swamps they may be so abundant that you may wish to watch each step. All denizens of the swamp should respect the cottonmouth, as it eats a wide variety of prey. Rats, frogs, fish, and even other water snakes are documented food items. We’ll examine how to identify these other water snakes (banded, plain-bellied, northern and brown) in Part II.


Paul Hurtado said...

"I don’t advise you to get too close to a snake unless can you identify it..."
Decent binoculars with relatively close focus are great for checking out hard-to-ID and potentially venomous snakes. Nice close looks for beginners, without the risk of getting too close! :)

David Steen said...

That's an excellent suggestion Paul. Who says binoculars are just for birdwatching?

It's also a great way to find snakes basking along the shore before they see you and drop into the water.