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Pantherophis obsoletus

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Pantherophis obsoletus

Secure  (NatureServe)[1]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Suborder: Serpentes
Family: Colubridae
Genus: Pantherophis
Species:
P. obsoletus
Binomial name
Pantherophis obsoletus
(Say in James, 1823)
Synonyms[2]

Pantherophis obsoletus – also known as the western rat snake, black rat snake, pilot black snake, or simply black snake[3] – is a non-venomous species of Colubridae found in central North America. No subspecies are currently recognized.[4] Its color variations include the Texas ratsnake.[2] Not to be confused with the Eastern indigo snake (Drymarchon couperi) or the Eastern racer (Coluber constrictor), which are other North American snake species commonly called 'black snakes.'

Geographic range

Pantherophis obsoletus is found west of the Mississippi River, from eastern and southern Iowa southward through Missouri and Arkansas to western Louisiana, westward to eastern Texas, northward through Oklahoma and eastern Kansas to southeastern Nebraska.[5]

Aside from the usual variety that is black or has patches of black on a lighter background, color variations include the Texas rat snake, a brown-to-black variant, often with tinges of orange or red, that can be found in southern Oklahoma, Texas, and Louisiana.

Habitat

Rat snakes live in a variety of habitats; some overlap each other. Rat snakes are excellent climbers and spend time in trees. They live in habitats ranging from a rocky hillside to flat farmland.[6]

Preferred habitat

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; the snake is also 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.

Description

A black rat snake, Chatham County, North Carolina

Adults of Pantherophis 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).[7][8] They are the largest snake found in Canada. The record total length is 256.5 cm (8 ft 5 in),[9] making it (officially) the longest snake in North America.[8] 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).[citation needed] The body mass of this rat snake 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).[10][11][12]

Juveniles are strongly patterned with brown blotches on a gray background (like miniature fox snakes: P. gloydi, P. ramspotti, and P. 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.[13][14]

Common names

Other common names include: 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.[3]

Showing "kinked" threatened posture
Western Rat Snake swimming on water in North East Texas

Behavior

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 mammalian carnivores (including the American mink, which weighs no more than an adult rat snake) and large birds of prey (especially red-tailed hawks).[15] When startled, they may freeze and wrinkle themselves into a series of kinks. If they feel further threatened, they may flee quickly or tail vibrate (potentially 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.[16] 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.[17][18]

Feeding

Raiding a bluebird birdhouse

This species is a constrictor, meaning it squeezes its prey to the point of cardiovascular collapse due to obstructive shock, coiling around small animals and tightening its grip until they can no longer circulate blood and die of profound hypotension, 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.[13] One snake was observed to consume an entire clutch of Mallard eggs.[15] 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.[19]

Reproduction

Mating while climbing a tree

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 (1.4–2.4 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.[20] The hatchlings are 28–41 cm (11–16 in) in total length,[3] and they look like miniature fox snakes.[13]

Taxonomy

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.[21] In addition, because Pantherophis is masculine, the specific epithet becomes the masculine obsoletus.[22] The split of Pantherophis from Elaphe has been further confirmed by additional phylogenetic studies.[23][24]

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 western rat snake (Elaphe obsoleta, now Pantherophis obsoletus). However, these three species are not morphologically distinct and overlap in all examined morphological characters.[25] More recent investigations have indicated P. alleghaniensis and P. spiloides interbreed freely in Ontario.[26]

In 2008, Collins and Taggart[27] 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.[23] The justification for this nomenclatural change has been removed by more recent research.[24]

In captivity

Western rat snakes are popular as pets. Their size, calm temperament, and ease of care contribute to this popularity and they also occur in many mutations such as leucistic, albino, and scaleless. They enjoy hiding and burrowing which is usually accommodated with a loose substrate (such as aspen wood shavings or newspaper) and one or more hide boxes. Captive rat snakes are generally fed killed or stunned mice because captive-bred mice reduce the risk of exposing the snake to pathogens or live prey-induced injuries.

References

  1. ^ "Elaphe obsoleta ". Natural Heritage Information Centre. Ontario Ministry of Natural Resources. Archived from the original on March 22, 2012. Retrieved October 19, 2010.
  2. ^ a b Pantherophis obsoletus, The Reptile Database. www.reptile-database.org.
  3. ^ a b c Wright AH, Wright AA (1957). Handbook of Snakes of the United States and Canada. Ithaca and London: Comstock. 1,105 pp. (in 2 volumes) (Seventh printing, 1985) ISBN 0-8014-0463-0. (Elaphe obsoleta obsoleta, pp. 230-234, Figure 72 + Map 24 on p. 235).
  4. ^ "Elaphe obsoleta ". Integrated Taxonomic Information System. Retrieved 29 November 2006.
  5. ^ Powell R, Conant R, Collins JT (2016). Peterson Field Guide to Reptiles and Amphibians of Eastern and Central North America, Fourth Edition. Boston and New York: Houghton Mifflin Harcourt. xiv + 494 pp. ISBN 978-0-544-12997-9. (Pantherophis obsoletus, p. 388 + Figure 161 on p. 334 + Plate 36 on p. 335 + Map on p. 385 + Figure 180 on p. 386).
  6. ^ US National Zoo. "Black Rat Snake". Archived from the original on 25 August 2016. Retrieved 9 March 2014.
  7. ^ Eastern Ratsnake Archived 2017-05-06 at the Wayback Machine, Herps of Texas
  8. ^ a b Species profile: Minnesota DNR. Dnr.state.mn.us. Retrieved on 2012-12-19.
  9. ^ Conant R, Bridges W (1939). What Snake Is That? A Field Guide to the Snakes of the United States East of the Rocky Mountains. (with 108 drawings by Edmond Malnate). New York and London: D. Appleton-Century. Frontispiece map + viii + 163 pp. + Plates A-C, 1-32. (Elaphe obsoleta obsoleta, pp. 56-58 + Plate 8, Figure 23).
  10. ^ Found in Gaston county NC 8-21-19 species over 14’ in length. Pantherophis obsoletus obsoletus (Say, 1823). Reptilia.forumpro.fr. Retrieved on 2012-12-19.
  11. ^ Black Rat Snake Info. Qrg.northwestern.edu. Retrieved on 2012-12-19.
  12. ^ "Snakes". Herpetological Education & Research Project. Retrieved 2015-05-21.
  13. ^ a b c Schmidt KP, Davis DD (1941). Field Book of Snakes of the United States and Canada. New York: G.P. Putnam's Sons. xiii + 365 pp. (Elaphe obsoleta obsolete, pp. 148-150, Figure 40 + Plate 16, center, on p. 336).
  14. ^ Conant R (1975). A Field Guide to Reptiles and Amphibians of Eastern and Central North America, Second Edition. Boston: Houghton Mifflin. xviii + 429 pp. + Plates 1-48. ISBN 0-395-19977-8 (paperback). (Elaphe obsoleta obsoleta, pp. 193-194 + Plate 28 + Map 149).
  15. ^ a b Eastern Ratsnake. Pantherophis alleghaniensis. Natural Heritage Endangered Program. mass.gov
  16. ^ Fact Sheet at Smithsonian National Zoological Park Website Archived 2016-08-25 at the Wayback Machine. Nationalzoo.si.edu. Retrieved on 2012-12-19.
  17. ^ Bent AC (1937). Life Histories of North American Birds of Prey. Part 1. Smithsonian Institution U.S. National Museum Bulletin, no. 167.
  18. ^ Bent AC (1938). Life Histories of North American Birds of Prey. Part 2. Smithsonian Institution U.S. National Museum Bulletin, no. 170.
  19. ^ Rat Snakes Archived 2012-11-22 at the Wayback Machine. Purplemartin.org. Retrieved on 2012-12-19.
  20. ^ Black snake profile at Smithsonian National Zoological Park website Archived 2016-08-25 at the Wayback Machine. Nationalzoo.si.edu. Retrieved on 2012-12-19.
  21. ^ Utiger U, Helfenberger N, Schätti B, Schmidt C, Ruf M, Ziswiler V (2002). "Molecular Systematics and Phylogeny of Old and New World ratsnakes, Elaphe Auct., and related genera (Reptilia, Squamata, Colubridae)" (PDF). Russian Journal of Herpetology. 9 (2): 105–124.
  22. ^ Elaphe obsoleta Archived 2009-04-14 at the Wayback Machine at The Center for North American Herpetology. Accessed 20 June 2008.
  23. ^ a b Burbrink FT, Lawson R (2007). "How and when did Old World ratsnakes disperse into the New World?". Molecular Phylogenetics and Evolution. 43 (1): 173–189. doi:10.1016/j.ympev.2006.09.009. PMID 17113316.
  24. ^ a b Pyron RA, Burbrink FT (2009). "Neogene diversification and taxonomic stability in the snake tribe Lampropeltini (Serpentes: Colubridae)". Molecular Phylogenetics and Evolution. 52 (2): 524–529. doi:10.1016/j.ympev.2009.02.008. PMID 19236930.
  25. ^ Burbrink FT (2001). "Systematics of the Eastern Ratsnake complex (Elaphe obsoleta)". Herpetological Monographs. 15: 1–53. doi:10.2307/1467037. JSTOR 1467037.
  26. ^ Gibbs HL, Corey SJ, Blouin-Demers G, Prior KA, Weatherhead PJ (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. S2CID 3727973.
  27. ^ Collins JT, Taggart TW (2008). "An alternative classification of the New World Rat Snakes (genus Pantherophis [Reptilia: Squamata: Colubridae])". Journal of Kansas Herpetology. 26: 16–18.

Further reading

  • Say T (1823). In: James E (1823). Account of an Expedition from Pittsburgh to the Rocky Mountains, Performed in the Years 1819 and '20, by Order of the Hon. J.C. Calhoun, Sec'y of War: Under the Command of Major Stephen H. Long. From the Notes of Major Long, Mr. T. Say, and other Gentlemen of the Exploring Party. Vol. I. Philadelphia: H.C. Carey and I. Lea. 503 pp. (Coluber obsoletus, new species, p. 140).
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