The Grey Ratsnake (Pantherophis spiloides) is a non-venomous constrictor in the Colubridae family. It is one of two species of Pantherophis ratsnakes, the other species being the much more common Eastern Foxsnake (Pantherophis vulpinus). Foxsnakes are widely distributed across the Lake Erie Region (including Rondeau, Pelee, and the Long Point Basin), as well as the east coast of Lake Huron’s Georgian Bay. Grey Ratsnakes are much more restricted in distribution, observed only within the Frontenac Arch (Cataraqui) region of southeastern Ontario, and Lake Erie’s Long Point Basin. Of these two ratsnake populations, the Frontenac is much larger and more secure. The Long Point population is very small and seriously imperilled. Thus the Frontenac population is listed as threatened, while the Long Point population is listed as endangered. There was historically a third population of Grey Ratsnakes in the Skunk’s Misery area of southwestern Middlesex, but their persistence into the present is unknown.

Description 

Grey Ratsnakes are Ontario’s largest snake species, growing to 180 cm in length. Grey Ratsnakes are usually a uniform black on the dorsal (back) side, which strongly contrasts with a white to cream underside and chin. However, some individuals, especially juveniles, may have dark grey or brown blotches on the back. The dark colouration of Grey Ratsnakes help with camouflage in the forest understory.

Within the Long Point Region, the Grey Ratsnake prefers dense deciduous forest habitat intermixed with more open habitats, such meadows and savannas. In Frontenac, they also are observed in rocky outcrops. Ratsnakes are adept climbers, often viewed on the bark or on the branches of trees when they are observed. This is a successful adaption to their woodland habitat, broadening the variety of prey accessible to Grey Ratsnakes. The home range an individual Grey Ratsnakes averages around 20 ha (50 acres), with males having larger territories than females. Between seasons, Grey Ratsnakes can travel substantially – up to 4 km from their hibernacula to their summer foraging grounds, twice per year. They tend to travel torwards areas with high populations of rodents.

Biology 

Grey Ratsnakes feed on a variety of prey, but most often rodents, such as deer mice (Peromyscus maniculatus), meadow voles (Microtus pennsylvanicus), woodland voles (Microtus pinetorum), and chipmunks (Tamias striatus). After capturing their prey, ratsnakes constrict their food before consuming it. They also consume bird eggs and nestlings. Predators of Grey Ratsnakes consist primarily of raptors (Acciptriformes, Falconiformes), and medium-sized carnivores (Carnivora), especially weasels (Mustelidae) and racoons (Procyon lotur), but they are not a preferred food item by any of these species. They are ectotherms – depending on the external environment to regulate body temperature. They actively seek sunny exposed areas to bask, but when temperatures become too warm, they seek shade in dense forests to avoid overheating. In the colder months, Grey Ratsnakes hibernate, congregating in communal hibernacula such as rock crevices, mammal burrows, or old building foundations to survive the winter.

Ratsnakes take around 10 years to reach their full size. At around 7-9 years, but sometimes earlier, female Grey Ratsnakes will reach sexual maturity. Mating occurs in the spring months – typically between April and June. Soon after, females will search for deposition sites to lay their eggs – typically in clutches of between 6-30 eggs in midsummer. Preferred areas for egg deposition include underneath decaying logs and rocks. Sometimes, multiple females will lay their eggs in a communal nesting site if the microhabitat is particularly suitable for this purpose. Eggs hatch after around 60 days, and the ~30 cm hatchlings emerge in September, not very much time before winter’s cold. This results in a high mortality rate in the first year due to physiological demands and predation. If they are not killed on roadways or predated, many Grey Ratsnakes can attain the age of 10-25 years.

To learn more about the biology of the Grey Rat Snake  – I would recommend reading Ontario Nature’s Reptile and Amphibian Atlas. Recently published in 2024, this ~300-page guide offers a plethora of comprehensive and informative content on herpetology, including detailed descriptions of the physical form and ecology of each species. Distribution maps are also provided for most species.

Distribution across North America

Across Eastern North America, the Grey Ratsnake forms a species complex with the Eastern Ratsnake (Pantherophis quadrivittatus), and the Western Ratsnake (Pantherophis obsoletus). These three species are divided by mountains and rivers! Between the Atlantic Ocean and Appalachian Mountains, the Eastern Ratsnake is the predominant species, extending from Vermont to southern Florida. In the Transappalachian region (between the Appalachians and the Mississsippi River), the Grey Ratsnake is dominant. This is our species at Long Point – occurring in the Great Lakes Region, the Appalachian Plateaus of Pennsylvania and West Virginia, with populations stretching southward to the Florida Panhandle. West of the Mississippi River, they are replaced by the Western Ratsnakes, extending to the eastern border of the Great Plains.

Fun facts 

• When threatened, they may rapidly vibrate their tail in leaf litter, mimicking the sound of a rattlesnake as a defensive bluff, even though they are non-venomous and lack rattles!
• Ratsnakes are well-named, having a beneficial role in controlling rodent populations in both natural and human-influenced environments, helping to keep numbers of mice and rats in check.
• Grey Ratsnakes have high site fidelity – returning to the same hibernacula for multiple winters. These are sometimes shared these with other snake species.
• The Latin genus name Pantherophis translates to “panther snake”, referring to their sleek, dark appearance as adults!

 

Written by Matthew Palarchio, HBSc in Environmental Sciences, Western University

Photo Credits (L-R):
© pelicankate, retrieved from Canva
© Adam Wander, retrieved from iNaturalist

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