Western rat snake
|Western rat snake|
(Say in James, 1823)
The western rat snake (Pantherophis obsoletus), also commonly known as the Texas ratsnake, black rat snake, pilot black snake, or simply black snake. is a nonvenomous colubrid species found in central North America. No subspecies are currently recognized.
The western rat snake is found west of the Mississippi River primarily in the states of Texas, Louisiana, Arkansas, Oklahoma, Kansas, Nebraska, Missouri, Iowa and Minnesota.
It prefers heavily wooded areas and is known for having excellent climbing ability, including the ability to climb the trunk of large mature trees without the aid of branches. This snake is a competent swimmer. During winter it hibernates in dens, often with copperheads and timber rattlesnakes. This association gave rise to one of its common names, pilot black snake, and the superstition that this nonvenomous species led the venomous ones to the den.
Adults can become quite large, with a reported typical length of 106.5–183 cm (3 ft 6 in–6 ft 0 in). They are the largest snake found in Canada. The record total length is 256.5 cm (8 ft 5 in), making it (officially) the longest snake in North America. Unofficially, indigo snakes (Drymarchon couperi) are known to exceed them, and one wild-caught pine snake (Pituophis melanoleucus), with a portion of its tail missing, measured 111 inches (2.8 m). The body mass of this rat snake is commonly 0.5 to 2.2 kg (1.1 to 4.9 lb) in large adults.
Juveniles are strongly patterned with brown blotches on a gray background (like miniature fox snakes, Pantherophis gloydi and Pantherophis vulpinus). Darkening occurs rapidly as they grow. Adults are glossy black above with white lips, chin, and throat. Sometimes traces of the "obsolete" juvenile pattern are still discernible in the skin between the scales, especially when stretched after a heavy meal.
Other common names include: Alleghany black snake, black chicken snake, black coluber, chicken snake, mountain black snake, mountain pilot snake, pilot, rat snake, rusty black snake, scaly black snake, cow snake, schwartze Schlange, sleepy John, and white-throated racer.
When not fully grown, rat snakes are subject to predation by many animals, including other snakes. Once they attain maturity, they are readily preyed on by humans, as well as mammalian carnivores (including the American mink, which weighs no more than an adult rat snake) and large birds of prey (especially red-tailed hawks). When startled, they may freeze and wrinkle themselves into a series of kinks. If they feel further threatened, they may flee quickly or vibrate their tails in dead leaves (a form of mimicry, which makes them sound like rattlesnakes). They are also capable of producing a foul-smelling musk, which they will release onto predators if picked up. They spread the musk with their tails in hopes of deterring the threat. When cornered or provoked, black snakes are known to stand their ground and can become aggressive. Counterattacks on large birds of prey, often committed by large snakes in excess of 150 cm (59 in) in length, have resulted in violent prolonged struggles. Utilizing its infamous agility and the great strength of its muscular coils, the black rat snake is sometimes able to overwhelm and kill formidable avian predators such as Red-tailed Hawks, Great Horned Owls and Red-shouldered Hawks, though in many cases the bird is able to kill the snake and both combatants may even die.
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 will often consume mice, voles, and rats, western rat snakes are far from specialists at this kind of prey and will readily consume any small vertebrate they can catch. Other prey opportunistically eaten by this species can include other snakes (including both those of their own and other species), frogs, lizards, chipmunks, squirrels, juvenile rabbits, juvenile opossums, songbirds, and bird eggs. One snake was observed to consume an entire clutch of mallard eggs. Cavity-nesting bird species are seemingly especially prevalent in this snake's diet. The rat snake has been noted as perhaps the top predator at purple martin colonies as a single large snake will readily consume a number of eggs, hatchlings, and adults each summer. Several rat snake repelling methods have been offered to those putting up martin houses, but most are mixed in success.
Mating takes place in late May and early June. The male snake wraps its tail around the female with their vents nearly touching. The male then everts one of its sex organs, a hemipenis, into the female sex organ, cloaca. The mating lasts a few minutes to a few hours. After five weeks, the female lays about 12 to 20 eggs, which are 36–60 mm (1.4-2 in.) long by 20–26.5 mm (0.8–1.1 in.) wide. The eggs hatch about 65 to 70 days later in late August to early October. The hatchlings are 28–41 cm (11–16 in.) in total length, and they look like miniature fox snakes.
This species has previously been placed (and is still placed by many) in the genus Elaphe, as Elaphe obsoleta. However, Utiger et al. found that Elaphe is broadly construed as paraphyletic, and placed this species in the genus Pantherophis. In addition, because Pantherophis is masculine, the specific epithet becomes the masculine obsoletus. The split of Pantherophis from Elaphe has been further confirmed by additional phylogenetic studies.
In 2001, Burbrink suggested this species be divided into three species based on geographic patterns of mitochondrial DNA diversity. He assigned new common names and resurrected old scientific names, resulting in the following combinations: eastern ratsnake (Elaphe alleghaniensis, now Pantherophis alleghaniensis), central ratsnake (Elaphe spiloides, now Pantherophis spiloides), and Gray Rat Snake (E. obsoleta). However, these three species are not morphologically distinct and overlap in all examined morphological characters. More recent investigations have indicated P. alleghaniensis and P. spiloides interbreed freely in Ontario.
In 2008, Collins and Taggart resurrected the genus Scotophis for Burbrink's three taxa, i.e., (Scotophis alleghaniensis), (Scotophis spiloides) and (Scotophis obsoletus) in response to the findings of Burbrink and Lawson, 2007. The justification for this nomenclatural change has been removed by more recent research.
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- Gibbs, H. L., Corey, S. J.; Blouin-Demers, G.; Prior, K. A. and Weatherhead, P. J. (2006). "Hybridization between mtDNA-defined phylogeographic lineages of black ratsnakes (Pantherophis spp.)". Molecular Ecology 15 (12): 3755–3767. doi:10.1111/j.1365-294X.2006.03056.x. PMID 17032272.
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|Wikimedia Commons has media related to Pantherophis obsoletus.|
- Pantherophis obsoletus at the Reptarium.cz Reptile Database. Accessed 2 June 2008.
- Ratsnake – Elaphe obsoleta at HerpNet. Accessed 2 June 2008.
- E. obsoleta image at Picasa. Accessed 2 June 2008.
- Elaphe obsoleta populations in Southern Ontario Canada Accessed 17 October 2008.
- Black Rat Snake at Natural Resources Canada
- "Black Snakes": Identification and Ecology – University of Florida fact sheet
- Black rat snake (Elaphe obsoleta obsoleta), Natural Resources Canada
- Scientific and Standard English Names of Amphibians and Reptiles of North America North of Mexico, With Comments Regarding Confidence In Our Understanding. Edition 6.1