Western Hog-nosed Snake - Heterodon nasicus
This is a heavy-bodied snake with a broad neck and dark blotches on the back extending from the back of the head onto the tail. There is a large amount of black pigmentation on the underside of the body, with contrasting patches of white, yellow, and orange. The anal scale is divided. The snout is upturned, with an enlarged rostral scale that is spade-like and keeled. The dorsal scales are also keeled. There are enlarged ungrooved teeth near the rear of the upper jaws. The maximum total length is about 90 centimeters, but most individuals are less than 65 centimeters. Hatchlings are similar to adults in appearance and about 17 to 20 centimeters total length. Eggs are smooth and elongate (usually 26 to 38 millimeters by 14 to 23 millimeters in length and breadth).
The presence of an upturned snout that is spade-like and keeled, in combination with keeled dorsal scales, a dark-patterned belly, a divided anal scale, and the absence of tail rattles and facial pit, distinguishes the Western Hog-nosed Snake from all other snakes native to Montana. The color pattern is described as similar to both the Gophersnake and the Prairie Rattlesnake, but neither of these, nor any other snake in Montana, has an upturned nose like the Western Hog-nosed Snake.
Summary of Observations Submitted for Montana
Number of Observations:
(Click on the following maps and charts to see full sized version)
Map Help and Descriptions
(Records associated with a range of dates are excluded from time charts)
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).
Little specific information for the state is available. They have been reported in areas of sagebrush-grassland habitat (Dood 1980) and near pine savannah in grassland underlain by sandy soil (Reichel 1995, Hendricks 1999).
In other locations, their apparent preference for arid areas, farmlands, and floodplains, particularly those with gravelly or sandy soil, has been noted. 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).
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 (high, medium, or low) of each of the 82 ecological systems mapped in Montana for
vertebrate animal species that regularly breed, overwinter, or migrate through the state by:
- 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 2001, Adams 2003, and Werner et al. 2004);
- Evaluating structural characteristics and distribution of each ecological system relative to the species’ range and habitat requirements;
- Examining the observation records for each species in the state-wide point database associated with each ecological system;
- 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 associated as using 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 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.
High, medium, and low habitat quality was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species in the 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 assignments of habitat quality.
If you have any questions or comments on species associations with ecological systems, please contact Bryce Maxell at email@example.com
or (406) 444-3655.
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: http://mtnhp.org/requests/default.asp
) 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.
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- Commonly Associated with these Ecological Systems
Forest and Woodland Systems
Shrubland, Steppe and Savanna Systems
Sparse and Barren Systems
Wetland and Riparian Systems
Little is known about the food habits of this carnivorous species in Montana. Based upon research in other areas that this species is found, the Western Hog-nosed Snake is considered a specialist predator on toads, but other main items in the diet include lizards and reptile eggs, and to a lesser extent frogs, salamanders, snakes, birds, and mammals (Baxter and Stone 1985, Hammerson 1999); young eat proportionally more lizards and lizard eggs than do larger snakes, which sometimes eat birds and other snakes and items not eaten by the young (Platt 1969). It commonly uses its spade-like nose to dig up buried prey detected by odor, such as Painted Turtle and Yellow Mud Turtle eggs (Iverson 1990), and may use toxic saliva to subdue active prey.
Little information is available specific to Montana. However, Western Hog-nosed Snakes are known to be diurnal. Their active period extends primarily from late April to mid-October in 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 1995, Hendricks and Reichel 1998, Hendricks 1999). Population density was estimated at about 4 to 6 per hectares in Kansas pasture, about half of this was in an ungrazed area (Platt 1969).
The few confirmed predators include hawks (Buteo spp.), American Crows, and Coyotes (Platt 1969, Hammerson 1999). Predators of the Western Hog-nosed Snake in Montana have not been reported. When disturbed, Western Hog-nosed Snakes may flatten their heads and vigorously strike and hiss. If these methods fail to deter a threat, individuals may exhibit death-feigning behavior that includes writhing, rolling over on the back, letting the tongue hang from the mouth, and remaining limp. If turned right side up, individuals will immediately roll over on their backs again (Hammerson 1999). Montana individuals show this death-feigning behavior (Mosimann and Rabb 1952).
There is almost no information specific to Montana. A female collected in Toole County on July 20, 1950 contained seven eggs ready for laying (Mosimann and Rabb 1952).
Information from other locations indicate that Western Hog-nosed Snakes lay clutches of 3 to 23 eggs in shallow burrows or nests a few inches below the surface (Platt 1969). The eggs of a female obtained June 11 measured 13 by 27 millimeters (Stebbins 1954). Eggs are laid in May through August, depending on locality, but mainly during June and July. Females may oviposit in alternate years, and only half of the females in a population may lay eggs in any year. Eggs hatch in about two months; hatchling emergence peaks in late July and early August in Colorado (Hammerson 1999). They reach sexual maturity in the second year (Platt 1969). In a Kansas study, only about 30% of the population was as old as 4 years. Maximum longevity in natural conditions is about 8 years, but captive animals have lived two decades.
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) along the Missouri River between Fort Benton and the mouth of the Judith River (Cope 1879). This is no longer the case (Maxell et al. 2003); the few recent records suggest that the species is uncommon throughout Montana, although its status is largely unknown. Even though this snake is still encountered across its historical range, it is less abundant than in the 19th Century. This is probably due to extensive habitat loss associated with conversion of prairie to agricultural landscapes. As in other regions, an unknown percentage of local populations experiences road mortality, as many specimen and observation records are of road-killed individuals. Draining of prairie wetlands may have negative impacts on the prey (toads and frogs particularly, and perhaps turtle eggs) this snake prefers. Management in Montana for this species is hampered by a lack of basic information on abundance, food habits, and habitat associations, but is probably best effected for the long-term by protecting suitable prairie habitats from conversion to agricultural uses. No specific management activities are suggested at this time, but any nests and dens should be protected and left undisturbed.
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