Continuing the theme of the many myths and misunderstandings that surround Cottonmouth (AKA, Agkistrodon piscivorous) biology, I am going to spend some time debunking one of the most sacred falsehoods about the species. My hunch is that this piece may attract more aggravated comments and statements to the contrary than the other posts in the series but here it is anyway: Cottonmouths have not been documented north of southeastern Virginia. Sorry those of you from Pennsylvania, New York, Maryland, West Virginia (do I need to go on?), but those snakes you see in the water, either yesterday or when you were growing up decades ago, were not Cottonmouths. If you are not yet raging, let me continue. Furthermore, on the East Coast, Cottonmouths are generally restricted to the Coastal Plain. Sorry northwestern Georgia, eastern Tennessee, and western North and South Carolina, you don’t have Cottonmouths either. West of this region, Cottonmouths can be found along the Mississippi river northwards to the southern extent of Indiana and Illinois and west to central Texas, and Oklahoma. Here's a range map.
Growing up in the northeastern United States, I was often asked if I came across any moccasins in all the time I spent in the swamp. If I didn’t answer in the affirmative, this was likely to prompt stories about friends of friends who had been bitten by the species (perhaps by stumbling into a breeding ball).
Some of the confusion can of course be attributed to the common error of mistaking harmless water snakes for the venomous Cottonmouth as well the tendency to use “moccasin” when referring to any swimming snake. I tackle both issues here. In the southeastern United States, there are several different water snakes a Cottonmouth could be mistaken for but in the Northeast there is only one, the Northern Water Snake, Nerodia sipedon (pictured on the right).
Also, the close and superficially similar cousin of the Cottonmouth, the Copperhead, Agkistrodon contortrix, can be found in a wide area outside of the Cottonmouth’s range. It is likely there are some that view these snakes as the same animal, but the Copperhead is not aquatic like the Cottonmouth. Plus the Copperhead tends to have an hourglass patterning that is typically only visible on very young Cottonmouths.
Different species are adapted for different climates. Animals that depend on the external environment to regulate their internal body temperature, like reptiles, are sensitive to changes they're not used to. For example, it is very difficult for reptiles to survive when the temperature drops if they are used to hot and humid conditions. This is why some species introduced into muggy Florida and now flourishing there, like Green Iguanas or Burmese Pythons, don’t tend to do well elsewhere in the United States (and they may even get into trouble during unseasonably cold stretches in Florida). The conditions just aren’t right and their internal workings (that is to say, their physiology) shut down. Summer might be nice but the party is over once winter comes.
The same is true for Cottonmouths, they are used to warmer conditions than the northeastern United States (for one example) can offer. Therefore, although it is in theory possible for a Cottonmouth to start crawling north from Virginia once summer hits, they won’t get far by the fall. Similarly, one could conceive of someone catching a cottonmouth and dropping it off in Pennsylvania (for some reason), and that animal might be as happy as a snake in mud during July…but the fun won’t last. And there’s no realistic scenario that would allow for a population of Cottonmouths to persist in these areas.
I understand that this runs counter to some deep-seated beliefs about the natural world around us so I am open to the possibility of Cottonmouths being found in unusual areas. I am prepared to believe you if you want to tell me you found a Cottonmouth in an Ohio swamp, but please don't think me rude if I ask for a photograph first.
Edit: A number of commenters have reported seeing Cottonmouths throughout Virginia. This isn't outside the realm of possibility but we need a picture to prove they're there.
I wrote about how these snakes are quick to show up when a lot of toads (= food) appear here. I've also written about accompanying Cottonmouth researchers as they wade through swamps to catch snakes in the spring as the reptiles try to take advantage of the new warmth and at night in the summer as the venomous snakes swam around me. Finally, I provide some tips on recognizing Cottonmouths from non-venomous watersnakes here.
Cottonmouth pictures provided courtesy of Fingerprince Prints.
Much of what I write is based on my experience in the field, however I also rely on the research of others, citations of some relevant scientific articles are below.
Blem, C., & Blem, L. (1995). The Eastern Cottonmouth (Agkistrodon piscivorus) at the Northern Edge of Its Range Journal of Herpetology, 29 (3) DOI: 10.2307/1564989
Dorcas, M., Willson, J., & Gibbons, J. (2010). Can invasive Burmese pythons inhabit temperate regions of the southeastern United States? Biological Invasions DOI: 10.1007/s10530-010-9869-6