The water moccasin (Agkistrodon piscivorus) and the cottonmouth (Agkistrodon piscivorus) are two venomous snake species found in the southeastern United States. They are often confused with each other as they have similar appearances and habitats. However, there are some key physical differences between them that can help identify them.
Being able to distinguish a water moccasin from a cottonmouth is important for safety reasons. Both snakes have potent venom that can cause severe tissue damage in humans if bitten. Knowing how to identify them allows you to exercise appropriate caution if you encounter them in the wild.
Geographic Ranges
The water moccasin has a more limited geographic range than the cottonmouth. Water moccasins are found exclusively in the southeastern United States, along the Atlantic Coastal Plain from southern Virginia to central Florida and westward to Texas.
Cottonmouths have a larger range that extends further westward and southward. They are found throughout the southeastern states, including along the Gulf Coast. Their range extends from southeastern Virginia through most of Florida and west to central Texas, Oklahoma, and southern Illinois.
So if you are outside the southeastern coastal states, any venomous water snake you encounter is likely to be a cottonmouth rather than a water moccasin based on geographic range alone.
Habitats
Water moccasins and cottonmouths occupy similar aquatic habitats, including marshes, swamps, ponds, lakes, rivers, and streams. However, water moccasins tend to favor slower-moving, murkier waters like swamps and marshes. Cottonmouths are more likely to be found in clearer waters with some current.
Cottonmouths also have a slightly wider habitat tolerance. While they prefer aquatic habitats, they may venture further away from water and can be found in drier areas like nearby forests, prairies, and fields. Water moccasins are more strictly aquatic and less likely to stray far from the water’s edge.
So if you spot a venomous water snake deep in the woods away from any water source, it is likely a cottonmouth rather than a true water moccasin based on typical habitat preferences.
Appearance
Water moccasins and cottonmouths share a stout body shape with thick midsections and a distinctly triangular head. But several key physical differences can help distinguish them:
| Physical Trait | Water Moccasin | Cottonmouth |
|---|---|---|
| Body pattern | Distinct dark brown or black crossbands on a lighter brown or olive background | Variable dark blotches on a brownish or olive background, little noticeable crossbanding |
| Head shape | Broad, more U-shaped from above | Flatter, more V-shaped from above |
| Tail pattern | Dark bands becoming half bands approaching the tail tip | May have faint banding but becomes solid towards the tail tip |
As the table summarizes, water moccasins have distinctive dark crossbands while cottonmouths have a more mottled, blotchy pattern. Water moccasins also tend to have a broader, more rounded head shape compared to the flatter, more triangular cottonmouth head. And juvenile cottonmouths have bright sulfur-yellow tail tips that fade to solid brown or black as adults.
So if you can get a close enough look, check for these physical differences. The distinctive crossbanding and U-shaped head are clear signs you are looking at a water moccasin rather than a cottonmouth.
Defensive Behaviors
Water moccasins and cottonmouths also differ slightly in their defensive behaviors when threatened:
– Water moccasins are more likely to stand their ground when confronted. They may coil up and open their mouths wide to expose the white lining as a warning sign.
– Cottonmouths prefer to flee if possible. But if cornered, they may rear up and throw their bodies into an S-shaped coil to display the white mouth lining.
So if the snake tries to escape rather than holding its ground, it points more toward a cottonmouth identity. And a coiled, upright S-shaped posture is also more characteristic of defensive cottonmouths.
However, there is still overlap in their behaviors. Either species may flee, coil up, or aggressively strike if provoked. So defensive behavior alone is not reliable for making a positive identification.
Venom Toxicity
One myth is that cottonmouths have more potent venom than water moccasins. But venom toxicity between the species is essentially equal. Both have evolved the same venom composition and potency to subdue aquatic prey like fish, frogs, and small mammals.
Studies that have directly compared cottonmouth and water moccasin venom find no significant differences in toxicity. Both venoms contain potent hemotoxins that damage blood cells and tissue. Envenomation symptoms are also identical between the species, including severe pain, swelling, necrosis, bleeding disorders, and potentially fatal cardio/neurotoxic effects in extreme cases.
So cottonmouths do not have more dangerous venom than water moccasins as is sometimes believed. Assume equal toxicity and lethality between the species if bitten.
Geographic Overlap
Water moccasins and cottonmouths both reside in the southeastern United States and their geographic ranges broadly overlap across the region. So it is possible to find both species living in close proximity in shared aquatic habitat.
In areas where their ranges overlap, follow the physical, behavioral, and habitat clues covered earlier to distinguish between them. Pay close attention to the presence or absence of clear dark crossbanding and the body shape. These are the most reliable visual markers for identifying water moccasins in areas where cottonmouths may also reside.
Safety Tips
The safest approach with any unknown snake across the southeastern United States is to keep your distance and leave it alone. But here are a few key tips if you encounter a snake and need to assess the risk:
– Look for key features like crossbanding and a very broad, U-shaped head to identify water moccasins.
– Eye the body shape and patterns to rule out harmless lookalikes like common water snakes.
– Note behaviors like coiling posture and willingness to flee or hold ground.
– Assume equal venom potency for safety no matter the species.
– Retreat and call for medical help immediately if bitten.
Proper identification is the first step. But give all venomous snakes their space and contact medical assistance promptly in the event you are bitten.
Conclusion
While water moccasins and cottonmouths share some habits and habitats, they can be distinguished from each other by range, physical traits, and defensive behaviors. Water moccasins have more distinct dark crossbanding and blockier heads while cottonmouths have more variable mottling and frequently gape to show the white mouth lining when threatened. Both should be treated warily and with ample distance. But proper identification can help assess the snake you have encountered and allow you to respond appropriately. With good awareness and caution, it is possible to coexist safely with these unique serpents.
