Montana Field Guide

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).

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.

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).

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).

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).

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).

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.

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).