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Sunday, May 13, 2012

Identifying snake sheds, part II

Not long ago, I posted about some techniques I used to identify a couple of snake sheds that I found in  Florida. I didn't plan a second post, because snake sheds are rarely found intact, but this week in southern Utah I had the opportunity to identify another snake shed, this one in nearly perfect shape. I found it snaked through the grass pointing at the opening of a burrow with an opening about the size of a quarter. Surely the snake had gone down the burrow, which led underneath a rock that was too large to lift (or else I would have!).

Habitat from the area
Despite being relatively fresh, the shed had already dried out, because it was extremely windy where I found it, at the base of a dam at Quail Lake State Park. In extricating it from the grass, I tore it at the midbody, which luckily didn't impair my ability to identify it later on. Importantly, the head was in perfect shape. I cupped it in my hands during the long walk back to the car, to prevent it being torn or blown away by the strong wind. As a result, I didn't get a chance to actually look at it closely for about half an hour, during which time a slew of possibilities ran through my mind as to what it could be. I am new to the southwest, so many of the species here are still unfamiliar to me. Because of what appeared to be a blunt head, as well as the overall small size (about 10 inches in SVL and 11.5 inches in total length), I first thought of a blindsnake, something I have wanted to see for quite some time. If the shed proved to be a blindsnake, I was prepared to recruit some serious help in lifting that rock. However, a glance through my fingers revealed differentiated ventral scales, which are characteristic of advanced snakes. I ruled out Scolecophidia.

Utah Blindsnake, Leptotyphlops humilis
There were many other possibilities, because the southwestern corner of Utah is in the Mojave desert, home to many species of reptiles that are not found in the rest of Utah. Another possibility that crossed my mind was the Southwestern Black-headed Snake, Tantilla hobartsmithi. Like the blindsnake, this species is adapted for burrowing. It is named for esteemed herpetologist Hobart Smith, who was born in 1912 and continues to conduct research and publish papers on reptiles and amphibians today, at age 99, despite having retired twice, in 1968 and 1983. Having published more than 1,600 manuscripts, Smith is the most published herpetologist of all time. He has described 102 species of reptile and amphibian, ranking 13th among all biologists in this regard.

Southwestern Black-headed Snake, Tantilla hobartsmithi
When the shed and I were safely in the car, however, I noticed that the head of my snake shed was not dark. Furthermore, the dorsal scales were boldly patterned with regularly-spaced dark blotches, twenty-eight in all (twenty-six on the body and two on the tail). The tail tip was broken, so I would guess that there were either thirty or thirty-one blotches in total. This was an important clue. The blotches were somewhat reminiscent of a kingsnake, milksnake, or long-nosed snake. However, they were restricted to the dorsal scales, rather than ringing the body as in king and milksnakes, and their edges were very clean, with no pattern in between, unlike the messier blotches of the long-nosed snake. Other options included the nightsnake and the glossy snake, but the blotches of my snake were very dark and regular, whereas these species have smaller, more irregular blotches.

Western Long-nosed Snake, Rhinocheilus lecontei
Finally, I turned to the scales for clues. As always, scale counts provide the most unambiguous evidence, although at this point I had a pretty good idea of what I thought it was. The dorsal scales were smooth and shiny, in 15 rows, and the subcaudal scales were divided, as was the anal plate. The head scales, most important, were somewhat reduced, consistent with a fossorial (burrowing) lifestyle. There were two postocular scales and only a single temporal scale in the first row, followed by two small temporals in the second row that I mistook for undifferentiated occipital scales at first. The upper labials were difficult to count, because the shed had already dried a little, and the snake had probably scraped it off using the labials as a leverage point. The same was true of the lower labials, but only a single pair of chin shields was evident.

Anterior part of the shed

Dorsal, lateral, and ventral views of the head

Rest of the body
After consulting some books to make sure I was right, I concluded that the shed belonged to a Ground Snake, Sonora semiannulata. These small snakes are highly variable in their body coloration and pattern, without consistent within-population variation. Although it is primarily restricted to the Mojave portion of Utah, records from the northeastern and central parts of the state suggest that it might be more widespread. It is found from southwestern Missouri west to southern California, north to Oregon and Idaho, and south to Mexico. Like other members of the tribi Sonorini, Ground Snakes eat mostly arthropods, including insects,  scorpions, spiders, and centipedes. Little is known about the species despite its wide range.

Ground Snake, Sonora semiannulata
It was exciting, almost forensic, to identify the shed of a species I had never seen before. Now I had a debate on my hands about whether to include it on my life list or not (a life list is a compilation of all the species of something - often birds, but in my case herps - that an individual has seen in their life). My friend Kerry Nelson and I have had lengthy discussions about what counts and what doesn't, including whether animals that others find are valid, whether dead animals are valid, and whether or not species seen in dreams (including those that exist only in dreams) are valid. What do you think? Would you count a shed, unambiguously identified, as seeing a species? I decided against it, but I'm very much looking forward to finding a live ground snake so I can add it to the list!


I would like to thank Brian EagerMatthijs Hollanders, Pierson Hill, and William Flaxington for use of their photographs.


Cox DT, WW (1995) Snakes of Utah. Bean Life Science Museum, Provo, UT

Ernst CH, Ernst EM (2003) Snakes of the United States and Canada. Smithsonian Institution Press, Washington D.C.

Uetz P (2010) The original descriptions of reptiles. Zootaxa 2334:59-68 <link>

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Life is Short, but Snakes are Long by Andrew M. Durso is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

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