Relax, Virginia. Unless that creek is in the southeastern part of the state, the Dismal Swamp in particular, your visitor is almost certainly the completely harmless brown water snake (Nerodia taxispilata) that’s found statewide, and not a water moccasin, a.k.a. cottonmouth, a.k.a. the semi-aquatic pit viper Agkistrodon piscivorus. It’s a common mix-up. So common, in fact, that one former naturalist for a southeastern park reported nearly 200 snakes that fishermen presented to him throughout two summers, proud of having killed the “evil, poisonous, venomous, aggressive, dastardly cottonmouths.” None of them—not one—was a cottonmouth; all were brown water snakes.
Sure, the two species are similar: Both are hefty and brown, and the cottonmouth’s markings vary too much to help distinguish them at a glance. Still, the differences are significant—if one dares get close enough to check. Between its eye and nostril, on each side of its face, the cottonmouth has the telltale heat-sensing “pit” that marks it as a pit viper. While the brown water snake has round pupils, the pupils of the moccasin are vertical and catlike. Easier to see is the shape of the head: Is it narrow, flowing into the body? Brown water snake. Or is it the wedge shape that marks poisonous snakes? There are also obvious differences of behavior. Brown water snakes do (excitingly!) enjoy basking high in a tree overhanging water, while cottonmouths prefer logs and rocks near water. When a cottonmouth swims, you can see most of its body undulating on the water’s surface, head poking up; the brown water snake swims underwater.
Perhaps the most obvious difference between the snakes is how they respond to disturbance. The brown water snake invariably skedaddles, whereas the cottonmouth curls up, rears its head back and opens its mouth wide, exposing that signature cottony-white maw: “Bring it on.”
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