| Pantherophis obsoletus | |
|---|---|
 | |
| Western rat snake swimming on water in northeastern Texas | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | Squamata |
| Suborder: | Serpentes |
| Family: | Colubridae |
| Genus: | Pantherophis |
| Species: | P. obsoletus |
| Binomial name | |
| Pantherophis obsoletus | |
| Synonyms[4] | |
| |
Pantherophis obsoletus, also knowncommonly as thewestern rat snake,black rat snake,pilot black snake, or simplyblack snake,[5] is a nonvenomousspecies ofsnake in thefamilyColubridae. The species is native to centralNorth America. There are nosubspecies that are recognized as being valid.[6] Its color variations include theTexas rat snake.[4] Along with other snakes of the eastern United States, like theeastern indigo snake (Drymarchon couperi) and theeastern racer (Coluber constrictor), it is called “black snake”.
P. obsoletus is found west of theMississippi River, from eastern and southernIowa southward throughMissouri andArkansas to westernLouisiana, westward to easternTexas, northward throughOklahoma and easternKansas to southeasternNebraska.[7]
Aside from the usual variety that is black or has patches of black on a lighter background, color variations includetheTexas rat snake, which is a brown-to-black variant, often with tinges of orange or red, that can be found in southern Oklahoma, Texas, and Louisiana.
Rat snakes of thegenusPantherophis are primarily diurnally-active and live in a variety of habitats; some overlap each other. They have adapted to a variety of habitats, including bayou, prairie, and rock outcrops, but they seem to have a particular preference for wooded areas, especially oak trees. They can also adjust their waking schedules in different habitats and exhibit facultative nocturnal behaviors[8]. Rat snakes are excellent climbers and spend a significant amount of their time in trees. The black rat snake is also a competent swimmer.
During winter it hibernates in shared dens, often withcopperheads andtimber rattlesnakes. When found in homes, often in groups. 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 ofP. obsoletus can become quite large, with a reported typical total length (including tail) of 106.5–183 cm (3 ft 6 in – 6 ft 0 in).[9][10] It is the largest snake found inCanada. The record total length is 256.5 cm (8 ft 5 in),[11] making it (officially) the longest snake inNorth America.[10] Unofficially, indigo snakes (genusDrymarchon) are known to exceed it, and one wild-caught pine snake (Pituophis melanoleucus), with a portion of its tail missing, measured 111 inches (2.8 m).[citation needed] The body mass ofP. obsoletus can range up to 0.5 to 2.2 kg (1.1 to 4.9 lb) in adults, although most adults are on the smaller end of this scale, per herpetology research sites, with weights most commonly between 0.77 and 1 kg (1.7 and 2.2 lb).[12][13][14]
Juveniles are strongly patterned with brown blotches on a gray background (like miniature fox snakes:P. gloydi,P. ramspotti, andP. 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.[15][16]
Other common names forP. obsoletus include: gray rat 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.[5]
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 bymammalian carnivores (including theAmerican mink, which weighs no more than an adult rat snake) and largebirds of prey (especiallyred-tailed hawks).[17] When startled, they may freeze and wrinkle themselves into a series of kinks. If they feel further threatened, they may flee quickly ortail vibrate; although this act of tail vibration is indeed a behavior that rat snakes share withrattlesnakes, it is not a form ofmimicry, as researchers have observed that snakes have used this method of tail vibration as a defense mechanism against predation long before the emergence of rattlesnakes.[18] 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.[19] 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 asred-tailed hawks,great horned owls andred-shouldered hawks, though in many cases the bird is able to kill the snake and both combatants may even die.[20][21]
P. obsoletus is aconstrictor, meaning it squeezes itsprey to the point of cardiovascular collapse due to obstructive shock, coiling around small animals and tightening its grip until the prey can no longer circulate blood and dies of profound hypotension, before being eaten. Though it will often consumemice,voles, andrats, the western rat snake is far from a specialist at this kind of prey and will readily consume any small vertebrate it can catch. Other prey opportunistically eaten by this species can include othersnakes (including both those of its own and other species),frogs,lizards,moles,chipmunks,squirrels, juvenilerabbits, juvenileopossums,songbirds, and bird eggs.[15][22] One snake was observed to consume an entire clutch ofmallard eggs.[17] Cavity-nesting bird species are seemingly especially prevalent in this snake's diet. The western rat snake has been noted as perhaps the top predator atpurple 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.[23]
InP. obsoletus 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, ahemipenis, into the female sex organ, thecloaca. The mating lasts a few minutes to a few hours. After five weeks, the female lays about 12 to 20eggs, which are 36–60 mm (1.4–2.4 in) long by 20–26.5 mm (0.79–1.04 in) wide. The eggs hatch about 65 to 70 days later in late August to early October.[24] The hatchlings are 28–41 cm (11–16 in) in total length,[5] and they look like miniature fox snakes.[15]
This species has previously been placed (and is still placed by many) in the genusElaphe, asElaphe obsoleta. However, Utiger et al. found thatElaphe is broadly construed asparaphyletic, and placed this species in the genusPantherophis.[25] In addition, becausePantherophis is masculine, thespecific epithet becomes the masculineobsoletus.[26] The split ofPantherophis fromElaphe has been further confirmed by additional phylogenetic studies.[27][28]
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, nowPantherophis alleghaniensis), central ratsnake (Elaphe spiloides, nowPantherophis spiloides), and western rat snake (Elaphe obsoleta, nowPantherophis obsoletus). However, these three species are not morphologically distinct and overlap in all examined morphological characters.[29] More recent investigations have indicatedP. alleghaniensis andP. spiloides interbreed freely in Ontario.[30]
In 2008, Collins andTaggart[31] resurrected the genusScotophis for Burbrink's three taxa (i.e.,Scotophis alleghaniensis,Scotophis spiloides, andScotophis obsoletus) in response to the findings of Burbrink andLawson, 2007.[27] The justification for this nomenclatural change has been removed by more recent research.[28]
The western rat snake is available captive-bred in the United States pet trade, and it has been bred for mutations such asleucistic,albino, and scaleless. However, it is not as popular as othercolubrids such as corn snakes, kingsnakes, milksnakes, and hognose snakes. Opinions vary on the western rat snake's disposition, but captive-bred individuals are reported to be more docile than their wild counterparts. With appropriate care, this species may be expected to live 15 years in captivity, and possibly more.
