Elaphe obsoleta
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| Elaphe obsoleta (Say In James, 1823) |
- Common names: black rat snake, pilot black snake, black snake.[1]
Elaphe obsoleta is a non-venomous colubrid species found in North America. It prefers heavily wooded areas and they are known for having excellent climbing ability, including the ability to climb the trunk of large mature trees without the aid of branches. No subspecies are currently recognized.[2]
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[edit] Description
This species is a constrictor, meaning it suffocates its prey, coiling around small animals and tightening its grip until they can no longer draw breath, before eating them. Though they do consume mice and rats, the Black Rat Snakes also willingly consume other snakes, chipmunks, squirrels, birds, and bird eggs.
Adults can become quite large and are known to reach up to eight (8) feet, being the largest snake found in Canada. The record length for a Black Rat Snake is 101 inches (2,600 mm), making it (officially) the largest snake in North America. Unofficially, Indigo Snakes are known to exceed them, and one wild caught Pine Snake with a portion of its tail missing measured 111 inches (2,800 mm).
When spotted by humans, Black Rat Snakes may freeze and wrinkle themselves into a series of kinks. If cornered, they may attempt to mimic rattlesnakes' behavior by vibrating the tip of their tail, giving a buzzing low-pitch sound. Black Rat Snakes are usually non-aggressive, but may strike at anyone who tries to capture or harm them. They are non-venomous and completely harmless.
[edit] Taxonomic issues
There are recent proposed, but not universally accepted, taxonomic changes for this species and the other North American members of Elaphe (suggested Pantherophis). Some taxonomists have suggested splitting what is now Elaphe obsoleta (suggested P. obsoletus) into three geographically separate species:
- Pantherophis alleghaniensis, Eastern Rat Snake. Range: east of Allegheny Mountains
- Pantherophis spiloides, Midland Rat Snake. Range: west of Apalachicola River and east of the Mississippi River
- Pantherophis obsoletus, Western Rat Snake. Range: west of the Mississippi River
Under this scheme, the color variations (Black Rat Snake, Yellow Rat Snake, Grey Rat Snake) do not correspond to subspecies. The color phases are considered to be a clinal variation in pigmentation with latitude or other climatic factors.
It should be noted that while a taxonomic suggestion has been made to change the genus Elaphe to Pantherophis, and this suggestion has been taken up by the web community at large, most herpetologists do not accept the suggestion and Herpetological Review 2003 34(3) rejected the taxonomic change. Several arguments against the change concerns the type of analysis used and the concept of "species" in biology.
- The Russian study that suggested the Old World and New World rat snakes were statistically significantly different was based on mitochondrial DNA evidence, not nuclear DNA.
- According to the concept of a species that is most commonly used in biology, if two populations can interbreed and produce viable, fertile and ecologically functional offspring, the two populations are the same species. Under this definition hybrids are, by definition, sterile and the product of crossing different species (at least). This genetic compatibility is based on nuclear DNA (nDNA). Mitochondrial DNA (mDNA) has nothing to do with compatibility of genomes and thus the functioning of a group as a single or multiple species.
- Since the mitochondrion is of bacterial origin (its chromosome is a single, circular chromosome like a bacterial chromosome) and lacks much of the proof reading apparatus found in the nucleus, it has a much higher mutation rate than nDNA. As long as the cytochrome system and the ATP generation apparatus still function, mutations in mitochondria can abound with little detriment to the cell. Thus wide diversity in mitochondrial sequences may be found while nDNA sequences may not be nearly as diverse.
- Since, in nature, biological species are most readily recognized by their ability to reproduce with each other, and that is a function of nDNA compatibility, examination of mDNA is useful to determine separation of populations, but not speciation since the mitochondria are not needed for genetic compatibility.
- Since the Russian study used mDNA instead of nDNA no relevance to the reproductive and nuclear genetic relatedness of the genera can be inferred from the data.
These references discuss some of the taxonomic issues.
- ITIS--listed as Elaphe obsoleta
- Center for North American Herpetology--discusses taxonomy
- Herpetological Review
- The Texas Rat Snake--from The Cold Blooded News, Newsletter of the Colorado Herpetological Society. This discusses the three proposed species split from E. obsoleta in detail.
- Flickr discussion on Rat Snake taxonomy--accessed April 22, 2006.
[edit] Photo gallery
 Found in Virginia at the beginning of summer 2004. |
 Black Rat Snake, face |
 Black Rat Snake kinking, or "crinkling" while stressed. |
 ventral surface |
 Found in Charlotte, NC late April '07. |
 Same Charlotte snake being released. |
 North Carolina specimen eating a rodent. |
[edit] Footnotes
- ^ Wright AH, Wright AA. 1957. Handbook of Snakes. Comstock Publishing Associates. (7th printing, 1985). 1105 pp. ISBN 0-8014-0463-0.
- ^ Elaphe obsoleta (TSN 174177). Integrated Taxonomic Information System. Retrieved on 29 November 2006.
[edit] External links
- Pantherophis obsoletus at the TIGR Reptile Database. Accessed 2 June 2008.
- Ratsnake - Elaphe obsoleta at HerpNet. Accessed 2 June 2008.
- E. obsoleta image at Picasa. Accessed 2 June 2008.
