Diamond-backed Water Snake juvenile (March 24, 2007), Austin, Texas
(Nerodia rhombifer rhombifer) Non-poisonous, pugnacious (will bite if handled, and though the juvenile bite is harmless, that of the adult can produce painful, freely-bleeding wounds), beneficial
Photos courtesy of Kathy B.
The markings on the back of this species is often described as similar to a section of chain-link fencing. It also looks like a series of dark X's, on a lighter background, that are strung down the snake's spine from neck to tail, and that are supported laterally by dark vertical patches, edged faintly in white, that extend from the conjunction of each pair of X's downward to the belly. No other species of snake found in Texas has this unique marking.
Nerodian water snakes as a group are stout-bodied anatomically and pugnacious in disposition. Like the rat snakes, their personalities are necessary accouterments that insure they survive as active predators. With a small fellow like this one, such a personality is "cute", and laughable. As the youngster bites, its tiny teeth are hardly capable of inflicting even minor injuries. Older specimens, on the other hand, are just as pugnacious but their bites, like those of mature rat snakes, are capable of drawing blood and inflicting pain. The wound that is thereby produced, however, is of little significance once the bleeding stops. I have handled large specimens of this species without being bitten, but I always take precautions to limit the snake's range of motion--and a thick pair of leather gloves prevents the snake from leaving marks that would otherwise remind me to wear gloves next time...
A close-up of the head, cropped from the photo above, is shown below. This is the typical Nerodian head:
An enlargement of another photo of this snake, below, shows added details of the head. Notice the dark vertical markings on the light-yellow lips, especially as the lips flare near the neck, and the large eyes, with clearly round pupils, set in a gently sloping face that forms a semicircle from the jaw upward to the top of the head, then downward to the other side. The cottonmouth, which this snake is most often mistaken for, has an angular face with slit, vertical pupils (cat's eyes) set in vertical sides topped with a prominent brow-ridge. The top of the cottonmouth's head is not curved as with this snake, but is remarkably flat. This specimen is slightly deformed, either the result of injury or from a congenital disorder, that produces an unusual twist in the spine just below the neck, but the gross anatomy of the head seems typical for the species in all other respects.
It is not unusual for me to receive photographs of older specimens of this snake, as well as other non-poisonous Nerodians, that the sender strongly believes to be a poisonous western cottonmouth. Whenever I am on a field trip with a group and someone spots a Nerodian water snake on the bank of a river or stream, the typical report from the observer is "Look! A cottonmouth!" Interviewing such observers generally elicits the fact that, for the majority, the terms "water-snake" and "cottonmouth" are considered legitimate synonyms. In fact, however, except in certain locations where cottonmouths are unusually abundant, most water snakes are, on examination, non-poisonous members of the genus Nerodia.
If the snake is swimming in water, an easy way to determine if the snake is poisonous or not is to observe if it floats when at rest. A Texas snake that floats at rest is likely a western cottonmouth (remember "cotton floats") or a rattlesnake, as Nerodian water snakes do not float, even at rest, though their spines may come close to the surface when they swim vigorously. Rattlesnakes, like the cottonmouth, swim with their bodies slightly submerged, and float with their bodies above the surface of the water when at rest.
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