Species Agkistrodon piscivorus leucostoma, Western Cottonmouth

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Last Updated June 09, 2007

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Agkistrodon piscivorus leucostoma

Western Cottonmouth

This is a western cottonmouth, Agkistrodon piscivorus leucostoma. This species is found in the southeastern United States and is sometimes also called water moccasin. Just about any aquatic situation with a vegetated shoreline and objects for basking prey is a potential home for it. However, that doesn't mean that any snake found near the water is a cottonmouth, like many (or most) assume. Many unrelated, nonvenomous watersnakes are found in these same areas and are much more common. This particular cottonmouth was killed by my father, after almost accidentally stepping on it near a rice field. He had told me about killing several of them already this year so I asked him to bring one if he could get it without maiming it too badly. It struck his boot several times, but was unable to penetrate, before he stepped on it, rolled it over and shot its underside. It is about 30 inches long. The species is in the family Viperidae, also known as pit vipers, which also includes rattlesnakes and copperheads. The pit is a heat sensing organ for locating prey. Cottonmouths are well known for their tendency to stand their ground with their whitish mouths gaping wide open when approached or threatened, hence the name cottonmouth.

Though I already new the Identity of this species when I got it, I went through the key in the book, The Amphibians and Reptiles of Arkansas by Stanley Trauth et al to point out its distinguishing characteristics. Here are the steps I took:

1. Facial pit between eye and nostril (black arrow, above); eye pupil elliptical (and vertical); single row of subcaudal scales extending to near tip of tail (yellow arrow, above)...Family Viperidae.

2. Tip of tail lacking a rattle or button...Genus Agkistrodon

3. Dorsum lacking hourglass-shaped crossbands, but rather dark brown or black bands; head black with dark stripe behind eye, pale labial stripe (red arrow, above)...western cottonmouth

Below are pictures of the snakes long retractable fangs. Here is some more information about bites from these snakes and their venom.