Western rat snakes (Pantherophis obsoletus) are a wide-ranging Nearctic non-venomous species. Their native distribution extends throughout the central region of the United States, as far north as the southern extent of Minnesota, southward along the Mississippi River to the Gulf Coast. Their range encompasses southeastern Iowa, Missouri, Arkansas, and the extent of Louisiana west of the Mississippi River. Western rat snakes are found as far west as the southern extent of Nebraska and eastern halves of Kansas, Oklahoma, and Texas. (Burbrink, 2001; Fitch, 1963)
Western rat snakes inhabit a variety of habitats in the central United States. They can be found on rocky hillsides and canyons, scrub/shrub fields, and prairie farmlands. They can also be found in temperate deciduous forests, swamps, woodland edges, and grasslands. Western rat snakes also inhabit dry or barren woodlands and sandy prairies. They also use rural anthropogenic habitats such as abandoned farmlands, homes, old oil fields, and caves. Due to their large geographic range, no exact elevational range has been designated. (Burbrink, 2001; Fitch, 1963; Gibbons and Dorcas, 2015)
Western rat snakes have rounded heads with no distinct snout. Their ventral scales are a creamy white color and their dorsal scales are a glossy black color, often with speckles of brown, orange, or yellow. Western rat snakes have weakly keeled scales that are otherwise smooth, similar to eastern rat snakes (Pantherophis alleghaniensis).
Western rat snakes possess slender bodies and adults have a snout-vent length (SVL) between 96 cm and 154 cm. At maturity, males are typically larger than females; Adult males range in SVL from 108 to 154 cm and adult females range in SVL from 96 to 120 cm. Adult males weigh 800 to 1,000 g, while adult females weigh 600 to 700 g.
Western rat snake hatchlings range in SVL from 29 cm to 37 cm and their weight ranges from 12 to 14 g. As juveniles, western rat snakes often exhibit a more grayish color with tan blotches; their scales darken as they mature. Juveniles also possess smooth, weakly-keeled scales.
Western rat snakes have distinct checkerboard patterns on their bodies that differentiate them other rat snake species in the genus Pantherophis. They are also longer than other rat snakes, and are one the longest snake species in North America. (Fitch, 1963; Gibbons and Dorcas, 2015; Linzey and Clifford, 1981; Mitchell, 1994)
Western rat snakes are oviparous, and eggs incubate for 65 to 70 days before hatching. Most early development occurs within the egg, with yolk providing energy to developing embryos. After hatching, juvenile males measure around 36.8 cm and juvenile females measure around 29 cm. Hatchlings weigh approximately 14 g and 12 g for males and females, respectively.
Western rat snakes exhibit indeterminate growth, but grow most rapidly as juveniles, within the first 3 to 7 years after hatching. As juveniles, both sexes grow at a rate of 3.5 cm per month. However, this rate is slowed during colder months, when western rat snakes enter brumation. After western rat snakes reach sexual maturity, growth rates are reduced to approximately 2 cm per year, although males grow faster than females. Western rat snakes reach sexual maturity between 3 and 7 years old, but are considered sexually mature once they reach a certain snout-vent length (SVL). Males are considered mature at a SVL of 107 cm, and females are considered mature at a SVL of 96 cm. The maximum recorded lengths for western rat snakes were 154 cm for a male and 120 cm for a female. (Fitch, 1963; Gibbons and Dorcas, 2015; Zug, et al., 2001)
Males and females reach sexual maturity between 3 and 7 years old. They are polygynandrous, meaning both males ad females have multiple mates. At the beginning of the breeding season, adult males compete for the right to mate with females.
Western rat snakes have a complex courtship pattern, involving tactile and visual rituals. The process begins when an individual male approaches a female and the two touch snouts. In some cases, the female flees from the courting male, in which case the male pursues the female until the female stops and indicates its receptivity. The male then places its head atop the dorsal side of the female. The male maintains chin contact with the dorsal side of the female, then mounts the female by moving the rest of its body onto the dorsal side of the female. The courting male then shakes the trunk of its body, sliding and twisting to keep the female close. The male makes forward jerking movements towards the head of the female. The male also contracts its body in a specific pattern, creating caudocephalic waves that induces greater receptivity to insemination. Finally, the male wraps the end of its tail around the posterior portion of the female and inserts its hemipenis into the cloaca of the female. The mating male may bite the neck of the female to ensure successful insemination before the female leaves. After mating is complete, the male dismounts the female and assumes a coiled position. (Fitch, 1963; Gibbons and Dorcas, 2015; Gillingham, 1979)
Western rat snakes emerge from brumation around February, and their breeding season spans from April to June. If temperatures are warm enough in early fall, breeding season may extend later than June.
Female western rat snakes usually lay multiple clutches of egs during the mating season, with an average clutch size of 15 (range: 4 to 44 eggs). Gestation periods have not been reported for western rat snakes. The incubation period for eggs is around 65 to 70 days. Immediately after hatching, male juveniles weigh about 14 g and measure about 36.8 cm, while female juveniles weigh about 12 g and measure about 29.0 cm. Hatchlings are independent at birth. Male and female western rat snakes both reach sexual maturity between 3 and 7 years old. (Fitch, 1963; Gibbons and Dorcas, 2015; Gillingham, 1979; Zug, et al., 2001)
Male western rat snakes provide no parental care beyond the act of mating. Females build a nest for their eggs, but provide no parental investment beyond this. Western rat snakes are immediately independent upon hatching. (Fitch, 1963)
Western rat snakes raised in captivity are reported to live between 16 and 33.9 years. The lifespan of western rat snakes in the wild is not well documented. However, other members of the genus such as corn snakes (Pantherophis guttatus) have been reported to live up to 24 years in the wild. (Perkins, 1955; Slavens and Slavens, 2003)
Western rat snakes are solitary and will usually avoid confrontation if possible. If threatened, they either remain motionless or attempt to flee the situation. If cornered they coil their bodies and open their mouths to appear threatening. They may also rapidly vibrate their tails against nearby grass or leaves, which creates a rattling sound similar to that of a rattlesnake. If predators are not deterred by these threat displays, western rat snakes will strike and constrict around predators and emit a foul odor from their anal glands.
Western rat snakes communicate in part using pheromones. Males establish territories by secreting pheromones and females use pheromones to attract potential mates. Western rat snakes tend to be diurnal, especially during cooler spring months, but they become more active at night during the summer.
Western rat snakes are partially arboreal and are adept at climbing trees to prey upon birds or mammals nesting in tree hollows. Western rat snakes are also capable of swimming to reach prey or traverse their environment.
Western rat snakes seek shelter and brumate from October to February, using hollow trees, underground burrows, caves, tree stumps, or abandoned houses. They emerge from brumation around February, before breeding season begins. Western rat snakes do not travel far from where they brumate and nest, but rather inhabit one area consistently. (Durner and Gates, 1993; Fitch, 1963; Gibbons and Dorcas, 2015; Zug, et al., 2001)
Western rat snakes have an average home range of 117 square meters, centered around where they hibernate and nest. They will not actively defend their home ranges against other western rat snakes, although they establish territories using pheromone markings. (Durner and Gates, 1993; Fitch, 1963)
Western rat snakes communicate chemically through pheromones and other gland secretions, which have an array of uses including defense from predators and mate attraction. Western rat snakes usually secrete a defense pheromone in their dens and burrows which repels predators. Western rat snakes also use pheromones to create trails for other western rat snakes to follow towards high aggregation sites such brumation dens. Female western rat snakes produce pheromones to attract males. These specialized pheromones are unique to their species and are only recognized by other western rat snakes.
Male western rat snakes establish dominance through touch. When male rat snakes detect a pheromone trail from competing males, they will follow the trail to its source. Once they find each other, competing males glide parallel to each other with their heads raised high. This continues until one of the males pushes its head down onto the other, asserting its dominance. Male western rat snakes also use tactile senses to initiate the mating process with females. Males also bite females during the act of mating.
Western rat snakes lack external ears, but are capable of detecting high- and low-frequency seismic vibrations using their opercularis systems, or internal ears. Their opercularis systems also help detect the movements of prey and predators in their environment.
The eyesight of western rat snakes is limited and they are only able to see a limited array of colors. However, they are highly sensitive to UV light which has allowed them to adapt to low-light environments.
Western rat snakes rely heavily on smell to sense their environment. They flick their forked tongues out of their mouths to collect scent particles from the ground and air. They then withdraw their tongues and insert the forked portions into two openings on the roofs of their mouths. These openings lead to their Jacboson's organ, which they use to detect the direction of scents emitted by prey, predators, or other western rat snakes. (Burns and Penning, 2021; Gillingham, 1979; Gillingham, 1980; Zug, et al., 2001)
Adult western rat snakes feed upon mammals including prairie voles (Microtus ochrogaster), pine voles (Microtus pinetorum), western harvest mice (Reithrodontomys megalotis), white-footed mice (Peromyscus leucopus), house mice (Mus musculus), eastern cottontails (Sylvilagus floridanus), hispid cotton rats (Sigmodon hispidus), eastern woodrats (Neotoma floridana), and northern short-tailed shrews (Blarina brevicauda). They feed on various avian species and their eggs, including fledging blue jays (Cyanocitta cristata), mourning doves (Zenaida macroura), and eastern bluebirds (Sialia sialis). Western rat snakes also consume lizards such as common five-lined skinks (Plestiodon fasciatus) and other snakes (both conspecifics or other species). They also consume various species of amphibians (class Amphibia) including frogs, toads, and salamanders. A 1963 study on the diets of western rat snakes surveyed 45 individuals and found that 66% of their diet was mammals, 23% birds, 8% amphibians, and 3% reptiles. (Burbrink, 2001; Fitch, 1963; Weatherhead, et al., 2003)
Known predators of Western rat snakes include red-tailed hawks (Buteo jamaicensis), broad-winged hawks (Buteo platypterus), and eastern screech owls (Megascops asio). Other snake species also prey on western rat snakes, including copperheads (Agkistrodon contortrix), speckled kingsnakes (Lampropeltis holbrooki), eastern racers (Coluber constrictor), and Texas indigo snakes (Drymarchon melanurus erebennus). Mammalian predators include raccoons (Procyon lotor), long-tailed weasels (Mustela frenata), and coyotes (Canis latrans).
Western rat snakes have developed defense mechanisms such as cryptic coloration which helps them camouflage with their environment. A primary defense used by western rat snakes is kinking, where they appear motionless and bend their bodies at different angles. This kinking is a form of camouflage. When cornered, western rat snakes coil up, with their mouths open, and vibrate their tails against dry leaves or grass to create a rattling sound. If this does not work and they are directly attacked, western rat snakes constrict around predators and exude a foul odor from their anal glands. (DeGregorio, et al., 2015; Fitch, 1963; Gibbons and Dorcas, 2015)
Western rat snakes are primary and secondary predators in their ecosystems. They control populations of common mammal pests and nesting birds, including hispid cotton rats (Sigmodon hispidus), western harvest mice (Reithrodontomys megalotis), prairie voles (Microtus ochrogaster), blue jays (Cyanocitta cristata), mourning doves (Zenaida macroura), and eastern bluebirds (Sialia sialis). Western rat snakes serve as a food source for mammals such as racoons (Procyon lotor) and long-tailed weasels (Mustela frenata) and birds of prey such as red-tail hawks (Buteo jamaicensis), broad-winged hawks (Buteo platypterus), and eastern screech owls (Megascops asio).
Western rat snakes are hosts to parasites such as harvest mites (Trombicula alfreddugesi) that cause reddish encrustation between their scales. Western rat snakes also host various alveolate species, such as Hepatozoon quadrivittata, Hepatozoon spiloides, Hepatozoon horridus, and Hepatozoon sipedon, which are all acquired through mosquito vectors. These parasites reduce the red blood cell counts and reduce nutritional intake of rat snakes, resulting in reduced growth rates. Tapeworms such as Oochoristica eumecis have been reported in the small intestines of western rat snakes, causing inflammation and abnormal growth. Additional tapeworms include those in the genus Mesocestoides. Apicomplexans in the genus Sarcocystis also have been reported in Oklahoma, and coccidians including Eimeria zamenis were found in Arkansas populations. (Fitch, 1963; Lalley, 2004; McAllister, et al., 2016; McAllister, et al., 2014; McAllister, et al., 2017; McAllister, et al., 1993; Smith, 1996; Telford, et al., 2012)
Western rat snakes are popular in the pet trade, as they are considered low-maintenance and suitable for beginner snake owners. Western rat snakes are sold at prices ranging from 50 to 600 USD. (Hammerson, 2019; MorphMarket, 2022)
When threatened, western rat snakes will inflict a painful bite onto those it deems as a threat; the pain inflicted depends upon the size of the snake. However, western rat snakes are non-venomous and will only bite as an act of self-defense against a supposed threat. Full treatment of wounds inflicted by western rat snakes at a hospital will cost a person an estimated 2,058 USD on average due to lab costs and expenses. (Basher, et al., 2012; Burns and Penning, 2021; Gillingham, 1980)
Western rat snakes are a species of "Least Concern" on the IUCN Red List. They do not have special status on the U.S. federal list, CITES appendices, or the state of Michigan list.
There are currently no major threats to western rat snakes. However, some smaller populations have declined due to extensive deforestation, which leads to habitat loss and prey depletion. Habitat destruction due to human encroachment also makes western rat snakes susceptible to population losses. Western rat snakes are often mistaken for rattlesnakes because they vibrate their tails when threatened, causing people to mistakenly kill them.
State management agencies often complete surveys to identify the home ranges of western rat snakes to limit habitat destruction. There are education programs that inform the public on the positive impacts that western rat snakes have on ecosystems. These impacts include population control of common pest species that may affect farmers and homeowners.
Western rat snakes are a common snake species in the central United States. They exist in already-protected areas, and are thus afforded some basic levels of habitat protection. The pet trade should be regulated so that wild populations remain at healthy levels. (Burbrink, 2001; Burns and Penning, 2021; Gillingham, 1980; Hammerson, 2019)
Hunter Greer (author), Radford University, Sierra Felty (editor), Radford University, Bianca Plowman (editor), Radford University, Karen Powers (editor), Radford University, Victoria Raulerson (editor), Radford University, Christopher Wozniak (editor), Radford University.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
living in landscapes dominated by human agriculture.
Referring to an animal that lives in trees; tree-climbing.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
uses smells or other chemicals to communicate
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
union of egg and spermatozoan
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.
Animals with indeterminate growth continue to grow throughout their lives.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
marshes are wetland areas often dominated by grasses and reeds.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
the business of buying and selling animals for people to keep in their homes as pets.
chemicals released into air or water that are detected by and responded to by other animals of the same species
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them
scrub forests develop in areas that experience dry seasons.
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
Living on the ground.
A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.
A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.
A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.
movements of a hard surface that are produced by animals as signals to others
uses sight to communicate
young are relatively well-developed when born
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