The plains hog-nosed snake is similar to the dusty hog-nosed snake in appearance. The plains hog-nosed snake is small to medium sized, grayish tan, with a stout body. There is 1 row of dark brown blotches down the back, 2 rows of smaller dark spots along the sides, and an upturned snout. The number of dark blotches down the midline is more than 35 in males and more than 40 in females. There is usually a dark brown diagonal line through the eye to the angle of the jaw, and, behind it and rather parallel to it, another elongated dark brown blotch running along the side of the head onto the neck. The rostral (nose) scale is upturned and elongated, appearing shovel-like. This species' belly is wide, with a jet-black color that extends from the neck onto the underside of the tail; it is edged in yellow blotches on some individuals. The scales on the body are keeled, and the anal plate (the last belly scale, which covers the anal opening) is divided.
This species has always been quite rare in the state and has not been seen for many years; it has probably been extirpated from Missouri. It formerly occurred only in the far northwestern corner.
Like other hog-nosed snakes, this species has several interesting defensive behaviors, including hissing, puffing out its head, thrashing, opening its mouth, and "playing dead." Although hog-nosed snakes rarely bite people, a bite can be painful and result in slight bleeding, discoloration, and swelling at the site of the bite.
Similar species: Missouri has two other hog-nosed snakes:
- The eastern hog-nosed snake (Heterodon platirhinos) is the hog-nosed snake most frequently encountered in Missouri; it occurs statewide. Its coloration and its markings (or lack of markings) are quite variable. Its belly is lighter than the back; the underside of the tail is normally lighter than the belly.
- The dusty hog-nosed snake (H. gloydi) lives in the sandy or loose prairie and savanna soils in southeastern Missouri — far from the loess hill prairies where the plains hog-nosed snake once occurred. The dusty hog-nosed snake has only recently been rediscovered in Missouri. It is so similar to the plains hog-nosed snake that one of the best ways to identify it is to compare geographical distribution. The other way to tell them apart is by the number of dark upperside midline blotches (for the plains hog-nosed snake, more than 35 in males and more than 40 in females; and for the dusty hog-nosed snake, fewer than 32 in males and fewer than 37 in females).
Adult length: 15 to 25 inches; occasionally to 36 inches.
Restricted to a few counties in northwestern Missouri — if it still survives in our state. In North America, its overall range is from Saskatchewan and Manitoba south through the Great Plains to New Mexico and Texas. Disjunct populations occur in Illinois, Missouri, Iowa, and Minnesota.
Habitat and Conservation
This species is restricted to sandy, loose prairie soils in northwestern Missouri; sadly, it apparently is gone from our state.
Little is known about the natural history of this species in our state, with only three confirmed specimens from northwest Missouri. The plains hog-nosed snake resides in dry, sandy or loose soil in prairie and savanna habitats. In Missouri, it has been found where the steep loess hills meet the floodplain of the Missouri River.
In east-central Kansas, this species is mainly active during the day from late April to mid-October. The plains hog-nosed snake takes shelter in burrows it digs in sandy or loose soils, as well as mammal burrows. Such shelters are used at night during the active season and during the winter.
When threatened, this harmless species may react in a variety of ways. An individual may try to escape by crawling toward shelter; it may coil and try to hide its head; or it may hiss loudly, spread its head and neck, and strike at the intruder. If the intruder is persistent, the snake will writhe about, open its mouth, extend the tongue, regurgitate any freshly eaten food, roll on its back, and “play dead.” If left alone, the snake will eventually right itself and move away.
The plains hog-nosed snake locates its prey by sight and smell. It uses its upturned, shovel-like snout to dig prey out of a burrow. Although hog-nosed snakes are known for their toad-eating habits, they also consume many other amphibians, birds and their eggs, small rodents, and reptile eggs. Turtle eggs are commonly consumed by the plains hog-nosed snake throughout its range. This species is particularly adapted to eating toads due to its large mouth, flexible jaws, and pair of enlarged teeth at the rear of the mouth on the upper jaw. These teeth allow for maneuvering and presumably deflating puffed-up toads, as well as injecting a toxic saliva for subduing prey.
The plains hog-nosed snake is apparently extirpated from Missouri; the last documented specimen was from 1961. Although it was once present in our state, it has not been seen in decades and we have probably lost it. We can hope that a few may still occur in the loess hill prairies in our extreme northwestern counties. There have been some recent anecdotal reports of this species in the Kansas City area, but these reports lack documentation such as specimens or photographs.
The plains hog-nosed snake is a species of conservation concern due to restricted distribution and preference of a specialized habitat (sandy, loess hills) in northwest Missouri. Although this species has not been seen for many years in the state, it is important to keep a watchful eye for this secretive snake.
Its close relative, the dusty hog-nosed snake, is critically imperiled. Both are species of conservation concern.
The western hog-nosed snake complex (Heterodon nasicus) formerly consisted of three subspecies: the dusty hog-nosed snake (H. n. gloydi), Mexican hog-nosed snake (H. n. kennerlyi), and plains hog-nosed snake (H. n. nasicus). All three subspecies have been elevated to full species. Two of these new species occur in Missouri: the dusty hog-nosed snake in southeastern Missouri (considered critically imperiled), and the plains hog-nosed snake in northwestern Missouri (considered extirpated). With the elevation of the plains hog-nosed snake to a species, the common name "western hog-nosed snake" is no longer necessary and has been replaced by "plains hog-nosed snake."
Mating normally takes place in the spring, but some individuals will mate in autumn. In June or July, females lay 4–23 eggs in a shallow burrow in loose or sandy soil. The white or cream-colored eggs are elliptical with smooth leathery shells. Female plains hog-nosed snakes produce eggs on a biennial cycle. The eggs hatch in August or September with an incubation period of 50–60 days.
Sexual maturity is attained in 1 to 2 years in males and 2 to 3 years in females. An individual, which was caught as an adult, lived almost 20 years in captivity.
Human alteration of the landscape is the underlying cause of many species’ decline. Agriculture, urban sprawl, and road building break up historically large tracts of grasslands, degrading and separating the remaining fragments, shrinking and disconnecting animal and plant populations. The loess hill prairie ecological community where this species occurred in Missouri used to cover more acreage than it does now.
On the bright side, people have been working to preserve North America's remaining loess hill prairies, which occur in northwestern Missouri and western Iowa, and the eastern edges of Kansas and Nebraska. MDC, the Missouri Prairie Foundation, and other conservation groups have been purchasing and restoring these unique habitats that share many qualities of plant communities much farther west.
Although hog-nosed snakes rarely bite people, a bite can be painful and result in slight bleeding, discoloration, and swelling at the site of the bite. Bites do not pose significant danger to humans, but care must be taken when handling hog-nosed snakes.
As predators, dusky hog-nosed snakes serve to check populations of the animals they consume, particularly frogs and toads, but many other animals, too.
This snake's elaborate defensive behaviors, including the ability to spread its head and neck and the physical adaptations that allow it, are reminders that plenty of animals seek this species as prey: owls, hawks, crows, foxes, coyotes, and raccoons. The eggs and young are particularly vulnerable to predation.
The shovel-shaped snouts of hog-nosed snakes are interesting adaptations for snakes that live and burrow in sandy soils.
Missouri's loess hill prairies were the last known habitats for this species in our state. Although native prairies themselves are rare, loess hill prairies (also called dry loess/glacial till prairies) are rarer still, ranked as imperiled and critically imperiled. Less than 200 acres remain in the state. Found only in the northwestern corner, these natural communities occur on the tall, rugged, steep-sided hills and bluffs along the Missouri River formed long ago by wind-blown silt called loess.
Some of the distinctive plants in loess hill prairies are blue and hairy grama grasses, soapweed yucca, low milk vetch, downy painted cup (a relative of Indian paintbrush), nine-anthered dalea, purple locoweed, skeleton plant, dotted blazing star, and silvery scurfpea. Many of the plants in loess hill prairies, like the plains hog-nosed snake, are more common in the Great Plains and midgrass prairies to our west. Think of the landscapes of western Kansas, Nebraska, and eastern Colorado. The loess hills represent the far eastern edge of their ranges.
Why care about species on the margins of their overall range, or ones that live in populations separate from the large, main population? Aren't there plenty more plains hog-nosed snakes in the Great Plains states? Often, plants and animals occurring on the edges of their overall range have slightly different genetic characters than the rest of the group. These genetic traits may ultimately be useful in case the environment (including the climate) changes, or if a disease or other threat emerges, enabling the "edge" population to survive and continue the species. Sometimes, once they are studied carefully, "edge" populations turn out to be distinct subspecies or even different species than the larger group.