black hills redbelly snake
Originally published in January/February 2004 edition of S.D. Conservation Digest.
Text and Photos by Doug Backlund
I saw my first Black Hills redbelly snake in a lunch box about fifteen years ago. One of my coworkers on a Forest Service timber thinning crew caught the little snake and put it in another coworker's lunch box. They got the response they were expecting from everyone except me. I had never seen a snake like this one but I recognized it from the descriptions I had read in various field guides. It was a Black Hills redbelly snake, at that time considered to be rare in South Dakota.
Over the years, I have seen many of these fascinating snakes. They are actually quite common in some areas of the Black Hills. A researcher in Minnesota conducted a population study of redbelly snakes, capturing and marking over 1,500 individuals on 59 acres of habitat. Similar research has not been done in the Black Hills but it is likely that this snake is much more common than people realize.
In 1963, Hobart Smith described this snake as a distinct subspecies of the redbelly snake (Storeria occipitomaculata) and christened it Storeria occipitomaculata pahasapae. The nominal redbelly snake, Storeria occipitomaculata, is found throughout much of eastern North America but the distribution only extends west to eastern South Dakota. Later research by Carl Ernst, published in 1974, showed that a small percentage of the redbelly snakes in western Minnesota demonstrated characteristics of the Black Hills redbelly snake and that intergrades were present. Ernst felt that the subspecies in the Black Hills was isolated as recently as the end of the Pleistocene, some 10,000 to 50,000 years ago, when eastern areas of the northern plains were repeatedly glaciated and boreal forests were common to the west of the glaciation. Glaciation forced the redbelly snake west and the wetter and cooler climate of the time created habitat for it to colonize as far west as the Black Hills. Today over 300 miles of grasslands and farmland prevents exchange between the large eastern populations and the smaller Black Hills population.
Redbelly snakes are animals of moist, forested habitats, although some have been taken in moist grassland habitats. Most Black Hills records are from the northern hills or in the granitic/schist formations such as the Harney Peak area, where surface water is more abundant due to higher precipitation or less permeable bedrock. The high limestone plateau of the western Black Hills has few records. This may be due to the higher permeability of the bedrock that creates a drier habitat and is not as suitable for this snake. Good habitat has an abundance of shelter, such as logs, rocks, and thick ground vegetation. Winter is spent in communal hibernating sites, probably under large rocks or in rock crevices. One communal site was found near Hill City in 1993, when several hundred redbelly snakes were found under a large rock.
Sexual maturity is reached at two years of age. In late summer, females give birth to live young. Litter sizes range from one to twenty-one. The young snakes are about 3-4 1/2 inches in length, by adulthood they will reach a length of 8-10 inches. No other snake in the Black Hills has the bright red belly that gives this snake its name. The upper surface of the snake has variations of longitudinal stripes, usually four darker stripes with a larger light stripe down the middle of the back. These are very docile snakes that rarely attempt to bite, even if they did bite the jaws and teeth are too small to penetrate skin.
Redbelly snakes reportedly feed on soft-bodied animals such as slugs and earthworms. Many reports of prey items are from captive snakes that probably eat what they are offered rather than what they naturally hunt. Special behavioral and morphological adaptations allow redbelly snakes to extract snails from their shells. Snails are a major food source. Reports of slugs in the stomachs of wild redbelly snakes may actually be snails that were extracted from their shells. One herpetologist I know has raised Black Hills redbelly snakes and has tested prey selection by the snakes. He found that they selected the larger species of snails, especially favoring the terrestrial Black Hills Rocky Mountainsnail, Oreohelix cooperi, another endemic species in the Black Hills.
In turn, the snakes are prey for other animals. One was found in the stomach of an eight- inch rainbow trout caught in Castle Creek by Dave Ode and Jim Kilian in 1988. The redbelly snake is probably preyed upon by a wide variety of predators.
Although the Black Hills redbelly snake may be abundant in good habitat, loss of habitat can change that status quickly. Large areas of the Black Hills do not meet their habitat requirements. Redbelly snakes may turn up from time to time in poor habitat, but it takes quality habitat to sustain a population over the long term. Most biologists believe that the Black Hills redbelly snake is secure for now but as human pressure for resources and space increase, the status could change. Now is the time to preserve and manage habitat for this snake and other species associated with moist, undisturbed forests. After all, the Black Hills is the only place on the planet where the Black Hills redbelly snake is found.
Smith, Hobart M. 1963. The Identity of the Black Hills Population of Storeria occipitomaculata, the Red-bellied Snake. Herpetologica 19(1): 17-21.
Ernst, Carl H. 1974. Taxonomic Status of the Red-bellied Snake, Storeria occipitomaculata, in Minnesota. Journal of Herpetology 8(4): 347-351.
Rossman, Douglas A. and Patrick A. Myer. 1990. Behavioral and Morphological Adaptations for Snail Extraction in the North American Brown Snakes (Genus Storeria). Journal of Herpetology 24(4): 434-438.