- Also called:
- western rat snake or pilot black snake
- Related Topics:
- black snake
Black rat snake
Where is the black rat snake commonly found?
What do black rat snakes look like?
What do black rat snakes eat?
Is the black rat snake venomous?
Black rat snake, (Pantherophis obsoletus), heavy-bodied nonvenomous snake commonly found in the eastern and central United States. Previously identified as Elaphe obsoleta, the species is now recognized as Pantherophis obsoletus. A broader grouping of four North American rat snake species called the P. obsoletus complex comprises the western rat snake (P. obsoletus), Baird’s rat snake (P. bairdi), central rat snake (P. alleghaniensis), and eastern rat snake (P. quadrivittatus). The taxonomy of these species had been debated since the 19th century until genomic data resolved the issue in 2020. The complexity is further compounded by the use of common names such as black snake, black rat snake, and pilot black snake for more than one of these species. For the purpose of this article, black rat snake is used to refer to the western rat snake, for which the species complex is named.
- Kingdom: Animalia
- Phylum: Chordata
- Class: Reptilia
- Order: Squamata
- Family: Colubridae
- Genus: Pantherophis
Species of Least Concern
Distribution and habitat
This species is mostly found in a region west of the Mississippi River. Its distribution extends from southern Louisiana and southern and central Texas, northward to Oklahoma, and to central and eastern Kansas, southeastern Nebraska, southeastern Iowa, and southeastern Minnesota. Its distribution in the lower Mississippi River valley overlaps with that of the central rat snake. Here some level of hybridization has been observed between the two species.
Black rat snakes occupy an expansive range of habitats, from swamps and marshes to forests and fields. Deserted or undisturbed human-made structures such as farms and houses can be their dens as much as brush, caves, canyons, and rock cliffs. Hollow trees or logs, abandoned mammalian burrows, building foundations, and derelict wells often serve as their overwintering sites.
" height="20" alt="HEW Logo">
Physical features
An adult black rat snake has a glossy black back and a white underside, lips, chin, and throat. In some adults the black coloration may appear brownish or be replaced with irregular patches of black color. Toward the front the white belly may have black checkered patterns, whereas the rear is usually speckled with gray, brown, or yellow. Reddish skin is often visible in the gaps between the scales. Juveniles can be distinguished by their dark facial bands and gray or tan body patterned with black or brown blotches.
Gloger’s rule is an ecological principle formulated by the German evolutionary biologist Bernhard Rensch to describe the relationship between climatic conditions and pigmentation in animals. According to this rule, the body color of animals is darker in hot and humid climates than that of their counterparts in colder climates. This difference in coloration results from variations in the production of eumelanin (the melanin pigment responsible for black and gray shades) and pheomelanin (the melanin pigment responsible for reddish, brownish, and yellowish brown shades) in the animal’s body in response to differences in temperature and humidity. The production of only eumelanin decreases in hot, dry regions, resulting in reddish body coloration, whereas the production of both types of melanin is reduced in very cold regions, resulting in pale body coloration. Such color variations are thought to be associated with camouflage, protection against parasites and ultraviolet radiation, and the effects of pleiotropic genes (genes that influence more than one, usually unrelated, physical trait or phenotype).
Named for the German ornithologist and zoologist Constantin Wilhelm Lambert Gloger, the rule applies primarily to birds and mammals. However, insects such as the fruit fly and plants such as the silverweed cinquefoil have also been shown to conform to Gloger’s rule. Recent researchers have proposed revising the rule to focus solely on humidity and precipitation and to exclude temperature as a determining factor.
Research published in 2022 found that body coloration in the black rat snake and other North American rat snakes is influenced by temperature, with darker individuals more common in cooler regions. This supports the hypothesis that their coloration likely facilitates more efficient absorption of solar radiation and aids thermoregulation. Darker individuals of P. obsoletus are also associated with comparatively wetter environments—a pattern that experts suspect may be consistent with Gloger’s rule.
The species can grow to more than 250 cm (8 feet) in length, although the reported range is between 90 cm and 183 cm (about 3 to 6 feet). Adults can weigh anywhere between 0.6 and 1 kg (1.3 to 2.2 pounds). Males are larger than females.
Natural history
Diet and behavior
Rodents, small rabbits, birds, frogs, lizards, and bats form the primary prey of this species. These snakes kill their prey by constriction and then swallow it whole. They also steal eggs from bird nests. They are proficient at climbing and have been found in tree branches at heights of about 3–9 meters (10–30 feet). Although they become nocturnal when temperatures soar during summer, they are usually found to be active during daytime in the cooler spring and autumn seasons. Black rat snakes display brumation during winter, wherein their activity levels decrease in response to the cold.
The trusted destination for professionals, college students, and lifelong learners.
SUBSCRIBE
The common name pilot black snake is a misnomer, stemming from an old belief that the black rat snake led rattlesnakes and other snake species to favorable overwintering sites. This belief likely arose from the species’ habit of sharing such sites with other snakes.
When threatened, this species can attack in self-defense, although it tends to stay away from disturbances or lie still to avoid attention. An alarmed individual may coil its body and open its mouth in an attempt to appear more intimidating. It may also shake its tail, which produces a rattling sound upon striking nearby vegetation; the sound is reminiscent of that made by rattlesnakes. If the threat persists, the snake may bite its opponent, coil around it, and emit a foul-smelling secretion from its anal glands.
Reproduction and development
Black rat snakes can breed at any time during their annual active season and mate with more than one partner. Females typically lay 4 to 40 eggs, putting their nests under rocks or in logs or tree holes, usually between June and July. They do not incubate the eggs. Eggs hatch in about two to three months, and the young immediately start foraging by themselves. They become sexually mature between three and seven years old. Although the life span of the black rat snake in the wild is unknown, in captivity adult individuals may live for more than 30 years.
Importance, threats, and conservation
Members of the P. obsoletus complex acquired the epithet rat snake because of their ability to hunt and consume rodents. The generic name Pantherophis is derived from the Latin panthera, meaning “panther,” and the Greek ophis, meaning “snake,” and likely refers to the blotched pattern on these snakes as well as their quiet, pantherlike hunting habits. Their rodent-hunting ability makes them an important natural means of controlling rodent pests. A 1963 study, for example, found that 66 percent of the diet of black rat snakes consists of mammals. Black rat snakes are eaten by raccoons, weasels, coyotes, owls, hawks, and other snakes.
Habitat destruction threatens the species in some parts of its range. It occasionally faces danger from humans mistaking it for a rattlesnake. These snakes are popular pets, though experts caution against overexploitation caused by the unregulated pet trade. However, as of 2016 the species is considered to be of least concern by the International Union for Conservation of Nature and Natural Resources.