Western Hog-nosed Snake. Heterodon nasicus

Description: A small-to medium-sized snake, with a total length ranging from 400-900 mm. The snout-vent length of a large female is about 780 mm, while that of a large male is about 550 mm. This is a heavy-bodied snake. The rostral scale is keeled dorsally and turned sharply upward. There are no facial pits. The body scales are keeled. The anal scale is divided. There is no rattle at the end of the tail. Colour is light brown with three or four rows of dark brown blotches extending the length of the body on the dorsal surface. The pattern may be bold or faint. Smaller brown blotches occur along the sides. The throat is white and the venter is black or checkered black and white. In colour it superficially resembles Crotalus and Pituophis.

Variation: Females are larger than males. The tail of males is relatively longer than that of females, averaging twenty-two percent of the snout-vent length compared with fourteen percent for females. Males become sexually mature after one to two years, females after one-and-a-half to three years.

Natural history: Generally diurnal, but may also be active at night. Found in areas of friable soil and shows a preference for sandy locations and damp lowlands. It is found in sandy or gravelly areas with low-growing plants, sandhills, dry stream bottoms, of ten near areas of water in typical badlands country. Available habitat for this species has been much reduced by man's activities. The limiting factors affecting its distribution are soil and vegetation types, and proximity to water. The oddly shaped snout is used in digging.

Heterodon eats toads, frogs, salamanders, other snakes, lizards, turtles, small rodents and various invertebrates. Its posterior teeth appear to function in puncturing toads that have inflated them- selves. It is preyed upon by hawks, crows and coyotes. When molested it spreads a "hood" at the back of the head, hisses and strikes. It may, however, play dead in such circumstances, rolling on its back, writhing and then remaining motionless. It is very likely to bite if handled. It appears to be mildly venomous to its prey, but the venom has no demonstrable effects on man. It becomes active after soil temperatures reach about 15°C and in Alberta is most active in May, June and July. Males become active earlier than females, and both sexes are most active when air temperatures are very high. Individuals may live for eight years.

Reproduction: Mating and courtship behaviour are not known and have never been observed. Females lay between four and twenty- three eggs in the summer, with a mean of approximately nine. Each egg is about 31 x 22 mm. Females produce a clutch every other year. The eggs are laid in sandy soil at a depth of about 90 mm. The incubation period is about sixty days. In Alberta, egg laying occurs from the middle of June to the end of July. Hatchlings measure about 177 mm total length, with a snout-vent length of about 150 mm.

Distribution: In Alberta, the hog-nosed snake is limited to the short- grass prairie of the southeastern corner. It is found from the Montana border north to the Red Deer River, primarily east of Orion and Medicine Hat. It probably also occurs in suitable habitat as far north as the Drumheller area. Solid circles on the range map associated with this description indicate populations within the current range in Alberta. The solid triangle represents a report of this species by Moore (1953a) that lies far outside of any other reported occurrence in the province, and the solid square is a pre-1979 record that lies outside of the current range. Extralimitally, it occurs from southern Saskatchewan and southwestern Manitoba south through the plains states to San Luis Potosi, Mexico, and from central Montana and eastern Arizona in the west, east to central Illinois. The eastern limit comprises a suite of highly fragmented populations.

Conservation status: The hog-nosed snake has a very restricted range in southeastern Alberta and is now very infrequently encountered. It can be considered to be rare and intense study is needed to establish its actual status. Alberta Fish and Wildlife have been gathering data through a public awareness program.

Remarks: Three subspecies are recognized. Heterodon nasicus nasicus occurs in Alberta. This subspecies ranges southward to Oklahoma, northern Texas and New Mexico. This snake has been severely affected in its distribution by human activities, and it is now much less common than it once was.

Significant references: Cook 1970, 1977b; Fitch, 1985; Lewin 1963a; Moore 1953a; Pendlebury 1976b; Platt 1969; Wright and Didiuk 1998.