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Plains Hog-nosed Snake - Heterodon nasicus
Other Names:  Western Hog-nosed Snake

Image Copyright and Usage Information
Species of Concern
Native Species

Global Rank: G5
State Rank: S2
(see State Rank Reason below)


Agency Status
USFWS:
USFS:
BLM: SENSITIVE
FWP SWAP: SGCN2, SGIN

External Links

State Rank Reason (see State Rank above)
Species is found across eastern Montana in suitable habitat but is rarely observed within its range. Trend is not well studied, and threats are poorly characterized. They likely include habitat loss due to agricultural conversion, mortality from vehicles when basking on roads and persecution by people mistaking them for rattlesnakes. Collection for the pet trade may occur as well.
Plains Hog-nosed Snake (Heterodon nasicus) Conservation Status Summary
State Rank: S2
Review Date = 01/08/2025
How we calculate Conservation Status

See the complete Conservation Status Report
 
General Description
EGGS:
The eggs are white and smooth with an elongated shape. Size ranges between 26-38 mm (1-1.5 in.) long and 14-23 mm (0.6-0.9 in.) wide (Platt 1969, Iverson 1995 in Hammerson). The eggs of a female obtained in June measured 13 mm by 27 mm (0.5 by 1.1 in.) (Stebbins 1954). Eggs are typically laid in a shallow excavation during the month of July. Clutches contain 2 to 24 eggs (Ernst and Ernst 2003).

HATCHLINGS:
Hatchlings resemble adults in pattern but are generally brighter in color. They measure 14-20 cm (5.5-8 in) total length (Ernst and Ernst (2003).

JUVENILES AND ADULTS:
This is a stout, heavy bodied species with an enlarged rostral scale that is keeled and spade-like much like a digging spade or trowel. There are enlarged ungrooved teeth near the rear of the upper jaws. This species has a broad neck and dark blotches on the back extending from the back of the head onto the tail. The dorsal scales are keeled with 23 or fewer rows of dorsal scales at midbody (Hammerson 1999). The underside of the tail is primarily black with contrasting patches of white, yellow, and orange, and the prefrontal scales are separated by small scales.

Total length (TL) for males in Kansas averages 55 cm (21.7 in.) and 65 cm (25.6 in.) for females. Maximum TL is 154 cm (60.6 in.) (Ernst and Ernst 2003). Males typically have 35 or more grayish brown, deep cinnamon, or chocolate brown blotches along mid dorsal line between head and vent while females may have greater than 40 blotches (Walley and Eckerman 1999, Hammerson 1999). The anal plate and subcaudals are divided, while ventrals range from 129-147 in males and 139-156 in females (Walley and Eckerman 1999).

Diagnostic Characteristics
The Prairie Rattlesnake (Crotalus viridis) and the Gophersnake (Pituophis catenifer) have a similar banded or blotched body pattern. However, Heterdon nasicus has a unique and distinctive upturned snout and lacks a rattle.

Species Range
Montana Range Range Descriptions

Native
 


Range Comments
The Western Hog-nosed Snake is primarily found in the northern Great Plains, ranging from southern Alberta southward along to northeastern New Mexico and northern Oklahoma; northeasterly to Illinois, Wisconsin, and northwestern Indiana; and northwesterly to southern Manitoba (Ernst and Ernst 2003). Of the three subspecies of Western Hog-nosed Snake found in North America the subspecies that occurs in Montana is Heterodon nasicus nasicus. The remaining two subspecies occur well to the south of Montana from southwestern New Mexico, south into Mexico and in Missouri. H. n. nasicus is distributed primarily along the major river corridors in the Great Plains region of eastern and north-central Montana (Werner et al. 2004). The Western Hog-nosed Snake was relatively abundant in Montana during the late 19th Century, at least in some regions; in 1876 it was the third most common reptile (after the Prairie Rattlesnake and Greater Short-horned Lizard (Phrynosoma hernandesi)) along the Missouri River between Fort Benton and the mouth of the Judith River (Cope 1879). Currently in Montana, there are about 244 records from 26 counties east of the Continental Divide (MTNHP 2024).

Maximum elevation: 1,286 m (4220 ft) in Cascade County (Gerald Painter, personal communication, MTNHP 2024).

Observations in Montana Natural Heritage Program Database
Number of Observations: 252

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density

Recency

 

(Observations spanning multiple months or years are excluded from time charts)



Migration
No information is available for Montana. Marked individuals in Kansas were usually recovered during the same year within a few hundred meters of their previous capture site; occasionally individuals moved a kilometer or more between years (Platt 1969, Hammerson 1999).

Habitat
The Western Hog-nosed Snake prefers plains and savannahs with well drained sandy or gravelly soil where it can easily burrow or dig out prey. Populations throughout the range of the species appear to be highly correlated with coarse alluvial and marine soils/deposits (Webb and Eckerman 1998). Where soils are appropriate H. nasicus can also be found in semi-agricultural areas. However, areas of intensive cropping may reduce habitat availability (Hammerson 1999). They occupy burrows or dig into soil, and less often are found under rocks or debris, during periods of inactivity (Baxter and Stone 1985, Hammerson 1999, Stebbins 2003).

While specific habitat use in Montana has been little studied, it appears that preferred habitat in the state includes sandy alluvial beds and riverbanks as well as loose soil below sandstone outcrops (Werner et al. 2004). These habitat types are based on documented occurrences and predicted range of H. nasicus in Montana. They have been reported in areas of sagebrush-grassland habitat (Dood 1980) and near pine savannah in grassland underlain by sandy soil (Reichel 1995b, Hendricks 1999).

Ecological Systems Associated with this Species
  • Details on Creation and Suggested Uses and Limitations
    How Associations Were Made
    We associated the use and habitat quality (common or occasional) of each of the 82 ecological systems mapped in Montana for vertebrate animal species that regularly breed, overwinter, or migrate through the state by:
    1. Using personal observations and reviewing literature that summarize the breeding, overwintering, or migratory habitat requirements of each species (Dobkin 1992, Hart et al. 1998, Hutto and Young 1999, Maxell 2000, Foresman 2012, Adams 2003, and Werner et al. 2004);
    2. Evaluating structural characteristics and distribution of each ecological system relative to the species' range and habitat requirements;
    3. Examining the observation records for each species in the state-wide point observation database associated with each ecological system;
    4. Calculating the percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system to get a measure of "observations versus availability of habitat".
    Species that breed in Montana were only evaluated for breeding habitat use, species that only overwinter in Montana were only evaluated for overwintering habitat use, and species that only migrate through Montana were only evaluated for migratory habitat use.  In general, species were listed as associated with an ecological system if structural characteristics of used habitat documented in the literature were present in the ecological system or large numbers of point observations were associated with the ecological system.  However, species were not listed as associated with an ecological system if there was no support in the literature for use of structural characteristics in an ecological system, even if point observations were associated with that system.  Common versus occasional association with an ecological system was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species as represented in scientific literature.  The percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system was also used to guide assignment of common versus occasional association.  If you have any questions or comments on species associations with ecological systems, please contact the Montana Natural Heritage Program's Senior Zoologist.

    Suggested Uses and Limitations
    Species associations with ecological systems should be used to generate potential lists of species that may occupy broader landscapes for the purposes of landscape-level planning.  These potential lists of species should not be used in place of documented occurrences of species (this information can be requested at: mtnhp.org/requests) or systematic surveys for species and evaluations of habitat at a local site level by trained biologists.  Users of this information should be aware that the land cover data used to generate species associations is based on imagery from the late 1990s and early 2000s and was only intended to be used at broader landscape scales.  Land cover mapping accuracy is particularly problematic when the systems occur as small patches or where the land cover types have been altered over the past decade.  Thus, particular caution should be used when using the associations in assessments of smaller areas (e.g., evaluations of public land survey sections).  Finally, although a species may be associated with a particular ecological system within its known geographic range, portions of that ecological system may occur outside of the species' known geographic range.

    Literature Cited
    • Adams, R.A.  2003.  Bats of the Rocky Mountain West; natural history, ecology, and conservation.  Boulder, CO: University Press of Colorado.  289 p.
    • Dobkin, D. S.  1992.  Neotropical migrant land birds in the Northern Rockies and Great Plains. USDA Forest Service, Northern Region. Publication No. R1-93-34.  Missoula, MT.
    • Foresman, K.R.  2012.  Mammals of Montana.  Second edition.  Mountain Press Publishing, Missoula, Montana.  429 pp.
    • Hart, M.M., W.A. Williams, P.C. Thornton, K.P. McLaughlin, C.M. Tobalske, B.A. Maxell, D.P. Hendricks, C.R. Peterson, and R.L. Redmond. 1998.  Montana atlas of terrestrial vertebrates.  Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, MT.  1302 p.
    • Hutto, R.L. and J.S. Young.  1999.  Habitat relationships of landbirds in the Northern Region, USDA Forest Service, Rocky Mountain Research Station RMRS-GTR-32.  72 p.
    • Maxell, B.A.  2000.  Management of Montana's amphibians: a review of factors that may present a risk to population viability and accounts on the identification, distribution, taxonomy, habitat use, natural history, and the status and conservation of individual species.  Report to U.S. Forest Service Region 1.  Missoula, MT: Wildlife Biology Program, University of Montana.  161 p.
    • Werner, J.K., B.A. Maxell, P. Hendricks, and D. Flath.  2004.  Amphibians and reptiles of Montana.  Missoula, MT: Mountain Press Publishing Company. 262 p.

Food Habits
The Western Hog-nosed Snake is a carnivorous species that primarily uses sight and scent to detect prey (Ernst and Ernst 2003). Using the spade-like nose it digs up buried prey detected by odor, such as Painted Turtle (Chrysemys picta) and Yellow Mud Turtle (Kinosternon flavescens) eggs (Iverson 1990). Above ground prey such as lizards, and to a lesser extent frogs, salamanders, snakes, birds, and mammals (Platt 1969, Baxter and Stone 1985, Hammerson 1999) are seized with a wide-open mouth. Like other Heterodon species, H. nasicus consumes a relatively large percentage of amphibians, but fewer over all compared to other species in this genus. Amphibian prey includes those in the genera Anaxyrus (A. cognatus and A. woodhousii), Spea (S. bombifrons), and Scaphiopus. Heterodon spp. are adapted to eating toads using their large mouths, mobile maxillae, and elongated posterior maxillary teeth that hold and deflate inflated toads (Kroll 1976). Other food items include bird eggs, small mammals, and invertebrates (Ernst and Ernst 2003).

Ecology
The annual activity period for Western Hog-nosed Snake is typically between late April/early May and October for Colorado (Hammerson 1999). The active period in Montana is poorly documented, with records from mid-May to the end of September, and mostly from early June to early August (Mosimann and Rabb 1952, Reichel 1995b, Hendricks and Reichel 1998, Hendricks 1999). H. nasicus is diurnal, being active primarily in the morning and evening, and retreating to temporary burrows dug in loose soil with its snout at night (Platt 1969).

H. nasicus does not hibernate communally. By October individuals dig burrows below the frostline in sandy or course soil and enter hibernation until the following spring (Ernst and Ernst 2003). Emergence from hibernation typically occurs in April/May with males often wandering widely to seek out sedentary females by following scent trails (Ernst and Ernst 2003). Werner et al (2004) suggests that dispersal range in Montana is 200 yards or less per day. Studies in Kansas found a movement of 408 m (1,339 ft) in 17 days for a male during the breeding season (Platt 1969).

The Western Hog-nosed Snake contains slightly toxic saliva secretions, which have caused mild envenomations in some humans (McAlister 1963, Kapus 1964, Grogan 1974, Morris 1985). Predators include hawks (Buteo sp.), American Crow (Corvus brachyrhynchos), and Coyote (Canis latrans). Western Hog-nosed Snakes are well known for their “death feigning” defensive behavior where they vomit, exudes feces, roll over on its back, and extends its tongue from its mouth (Gehlbach 1970, Kroll 1977). If turned right side up, individuals will immediately roll over on their backs again (Hammerson 1999). Individual defensive behaviors vary among individuals, but Montana individuals have demonstrated this death-feigning behavior (Mosimann and Rabb 1952). Prior to death-feigning, they will often inflate their body, spread their necks, hiss, and pretend to strike. However, they almost never bite (Degenhardt et al. 1996).

Reproductive Characteristics
Mating generally occurs in May. However, some mating may occur late in the year and females have been found to store sperm over winter from fall mating (Ernst and Ernst 2003). Courtship behavior has not been described. Females may oviposit in alternate years, and only half of the females in a population may lay eggs in any year. Eggs are laid in shallow nests excavated to 10 cm (3.9 in.) in loose or sandy soil in July, with clutches containing 2 to as many as 24 eggs (Ernst and Ernst 2003). There is almost no information specific to Montana. However, a female collected in Toole County on July 20, 1950, contained seven eggs ready for laying (Mosimann and Rabb 1952). Hatching occurs from mid-August to mid-September with an estimated full incubation period of 30-60 days. Males reach sexual maturity between 2-3 years while females reach maturity between 3-4 years (Hammerson 1999). Maximum life expectancy in the wild appears to be approximately 8 years, but captive animals have lived two decades (Platt 1969). Population data for this species appears to be meager. However, Platt (1969) found two populations in Kansas as 57 and 121 snakes, with densities of 2.8 and 6.0/ha, respectively and only about 30% of the population was as old as 4 years.

Management
The following was taken from the Status and Conservation section for the Western Hog-nosed Snake account in Maxell et al. 2009.

Western Hog-nosed Snakes appear to be sparsely distributed in the Great Plains region of eastern and north central Montana. In addition, documented occurrences of the species in the state have declined in recent years, and the status of H. nasicus in Montana is uncertain (Werner et. al 2004). H. nasicus is currently listed as a species of special concern in Montana. However, it is unclear if this is simply due to 1) a lack of intensive surveys and secretive nature of the species, 2) limited and/or patchy distribution of suitable habitat and appropriate soils, or 3) an actual decline in this species abundance in Montana. The fact that this species does not typically reach sexual maturity until their third or fourth year may potentially contribute to naturally low population numbers. Risk factors relevant to the viability of populations of this species are likely to include conversion to intensive agriculture, amphibian prey declines, habitat loss/fragmentation, road and trail development, overgrazing, and use of pesticides and herbicides. However, perhaps the greatest risk to maintaining viable populations in Montana is the lack of baseline data on its distribution, status, and habitat use. These data are needed to monitor trends and recognize dramatic declines when and where they occur within Montana. Over its range, H. nasicus has apparently decreased in numbers and is now protected in several states (Ernst and Ernst 2003). Studies identifying or addressing specific risk factors for H. nasicus are lacking. However, documented studies and other issues pertaining to their conservation include the following: (1) Roads often have negative impacts on population size and distribution of snakes and other reptiles. High road density has been positively correlated to low population size, and restriction to roadless areas, which can lead to local extirpations (Rudolph et al. 1998, Jochimsen et al. 2004). While this has not been studied directly on H. nasicus in Montana, populations are probably affected in areas of high road density. A high percentage of observation records in Montana are road-killed individuals (MTNHP 2007). Similarly, many road-killed specimens have been observed in Alberta. Their tendency to bask on roads in morning hours makes them particularly vulnerable. However, their small home ranges and non-migratory habits make this less of a risk for populations in roadless areas (Wright and Didiuk 1998). (2) Little data exists on the effects of agricultural activities on H. nasicus; however, agricultural activities generally have significant negative impacts on snake habitat (Russell and Bauer 2000). Much of Montana’s native prairie is now under cultivation, with 5,589,905 hectares classified as agricultural lands in 1997 (Redmond et al. 1998). Furthermore, a recent increasing trend in cropland conversion is evident with 1.2 million acres of native prairie converted to cropland between 1982-1997, much of which is located within the natural range of H. nasicus. Wright and Didiuk (1998) suggest that in Alberta agricultural activities constitute the greatest risk factor to H. nasicus populations by destroying habitat which creates barriers to dispersal, by direct killing during plowing and harvesting activities, and by ingestion of pesticides and herbicides. (3) Wright and Didiuk (1998) suggests that oil and gas development in Alberta may pose a threat via roadbuilding, high traffic, and creation of long trenches which are known to trap other snake species. Coal Bed Methane Development may also pose similar threats via increased road development and traffic associated with development (Jochimsen et al. 2004). (4) There is evidence that the Western Toad (Anaxyrus boreas) and the Northern Leopard Frog (Lithobates pipiens) have experienced declines in western Montana, primarily from infections of Amphibian Chytrid Fungus (Batrachochytrium dendrobatidis) (Maxell 2000). If significant amphibian declines occur in eastern Montana from similar pathogens or other causes, it could pose an indirect threat (Wootton 1994) to H. nasicus populations by limiting a primary food source. (5) Western Hog-nosed Snakes are often mistaken for Prairie Rattlesnakes (Crotalus viridis) and intentionally killed due to their intimidating appearance and defensive behavior. Ranchers and farmers erroneously call this species the “puff adder” in many parts of their range and consider them dangerous (Degenhardt et. al 1996, Wright and Didiuk 1998).


References
  • Literature Cited AboveLegend:   View Online Publication
    • [MTNHP] Montana Natural Heritage Program. 2006. Point Observation Database. Montana Natural Heritage Program, Helena, MT. Accessed April 25, 2006.
    • Baxter, G.T. and M.D. Stone. 1985. Amphibians and reptiles of Wyoming. Second edition. Wyoming Game and Fish Department. Cheyenne, WY. 137 p.
    • Cope, E. D. 1879. A contribution to the zoology of Montana. American Naturalist 13(7): 432-441.
    • Degenhardt, W. G., C. W. Painter, and A. H. Price. 1996. Amphibians and reptiles of New Mexico. University of New Mexico Press, Albuquerque.
    • Dood, A.R. 1980. Terry Badlands nongame survey and inventory final report. Montana Department of Fish, Wildlife, and Parks and Bureau of Land Management, Helena, MT. 70 pp.
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    • Gehlbach, F.R. 1970. Death-feigning and erratic behavior in leptotyphlopid, colubrid, and elapid snakes. Herpetologica 26: 24-34.
    • Grogan, W.L., Jr. 1974. Effects of accidental envenomation from the saliva of the eastern hognose snake, Heterodon platyrhinos. Herpetologica 30: 248-249.
    • Hammerson, G.A. 1999. Amphibians and reptiles in Colorado. University Press of Colorado & Colorado Division of Wildlife. Denver, CO. 484 p.
    • Hendricks, P. and J.D. Reichel. 1998. Amphibian and reptile survey on Montana refuges: 1996. Montana Natural Heritage Program, Helena, MT. 19 p.
    • Iverson, J. B. 1990. Nesting and parental care in the mud turtle, Kinosternon flavescens. Canadian Journal of Zoology 68:230-233.
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    • Jochimsen, D.M., C.R. Peterson, K.M. Andrews, and J.W. Gibbons. 2004. A literature review of the effects of roads on amphibians and reptiles and the measures used to minimize those effects. Final Draft, Idaho Fish and Game Department, USDA Forest Service.
    • Kapus, E.J. 1964. Anatomical evidence for Heterodon being poisonous. Herpetologica 20(2): 137-138.
    • Kroll, J.C. 1973. Comparative physiological ecology of eastern and western hognose snakes (Heterodon platyrhinos and H. nasicus). Ph.D. Thesis, Texas A&M University 261p. 1973.
    • Kroll, J.C. 1977. Self-wounding while death feigning by western hognose snakes (Heterodon nasicus). Copeia 1977(2): 372-373.
    • Maxell, B. A. 2000. Management of Montana's amphibians: a review of factors that may present a risk to population viability and accounts on the identification, distribution, taxonomy, habitat use, natural history, and the status and conservation of individual species. Report to USFS Region 1, Order Number 43-0343-0-0224. University of Montana, Wildlife Biology Program. Missoula, MT. 161 p.
    • Maxell, B.A., P. Hendricks, M.T. Gates, and S. Lenard. 2009. Montana amphibian and reptile status assessment, literature review, and conservation plan, June 2009. Montana Natural Heritage Program. Helena, MT. 643 p.
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    • Mosimann, J.E. and G.B. Rabb. 1952. The herpetology of Tiber Reservoir Area, Montana. Copeia(1): 23-27.
    • Platt, D. R. 1969. Natural history of the hognose snakes Heterodon platyrhinos and Heterodon nasicus. Museum of Natural History. University of Kansas Publications 18(4): 253-420.
    • Redmond, R.L., M.M. Hart, J.C. Winne, W.A. Williams, P.C. Thornton, Z. Ma, C.M. Tobalske, M.M. Thornton, K.P. McLaughlin, T.P. Tady, F.B. Fisher, and S.W. Running. 1998. The Montana gap analysis project: final report. Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, Montana. xiii + 136pp. + appendices.
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    • Webb, R.G. and C.M. Eckerman. 1998. Neotype and type locality of the western hognose snake, Heterodon nasicus (Serpentes: Colubridae). Texas Journal of Science 50(2): 99-106.
    • Werner, J.K., B.A. Maxell, P. Hendricks and D.L. Flath. 2004. Amphibians and Reptiles of Montana. Mountain Press Publishing Company: Missoula, MT. 262 pp.
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  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
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Plains Hog-nosed Snake — Heterodon nasicus.  Montana Field Guide.  .  Retrieved on , from