Plains Hognosed Snake (Heterodon n nasicus )

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DISTRIBUTION:

Heterodon nasicus ranges from southwestern Manitoba, southern Saskatchewan, and southeastern Alberta, Canada, and wetsern Minnesota throughout the Great Plain to northern Zacatecas, San Luis Potosi, and Aguascalientes, Mexico. Relictual populations occur in southeastern Minnesota, northwestern Iowa, eastern Nebraska, western Illinois, northwestern and southeastern Missouri, central Wyoming, and northwestern Colorado.

HABITAT:

Western Hognosed snakes are restricted to the sandy soils of the short grass, mixed grass, and savanna communities in the west-central portion of the United States. Populations appear to be highly correlated with the presence of coarse alluvial and marine deposits (Eckerman 1996). In Arizona, Gloyd (1937) found this species restricted to the eastern plains area.

The northern distribution and that of relict populations in Illinois are limited by soil and temperature condition, and are closely associated with the Prairie Peninsula, as defined by Smith (1957) and Conant (1978).

DEFINITION

A small to medium heavy bodied species with males reaching up to 663 mm tail length, and females to 1540 mm. The ground color is brown, brownish grey or tan. A series of 23-52 grayish brown, deep cinnamon, or chocolate brown dorsal blotches occur on the dorsum and alternate with rows smaller, similarly colored spots on the sides. The head pattern consists of a dark band across the posterior azygous scales, the anterior edge of the frontals, and the supraoculars, as well as a broad dark band from the eye to the angle of the mouth. A middorsal and two lateral elongated nuchal blotches extend forward to the parietal scales. The venter is usually black with yellow blotches although it may be checkered with irregular white markings or appear pale with large black blotches.

Two to 28 small, irregular azygous scales separate the prefrontals from the frontal and internasals from the rostral. The rostral is sharply upturned and concave dorsally. The pre-, post-, and subocular scales form an ocular ring and range in number from 9-13. The anterior temporals number 2-5 and posterior temporals 3-7. Infralabials number 9-13, usually 10-11. The two large anterior chin shields are broadly in contact, whereas the posterior chin shields are reduced in size or absent. The anal plate (cloacal scute) and subcaudals are divided. Ventrals range form 129-147 in males and 139-156 in females. Subcaudals range from 35-50 in males and 26-41 in females. The dorsal body scales are keeled, with 21-26 rows anteriorly, 19-26 rows at midbody, and 16-23 rows anterior to the cloaca. The maxillla is short and deep, with the mesial process curving posteriorly toward the posterior process. About ten teeth occur on the maxilla, four on the palatine, nine of the pterygoid, and fourteen on the dentary.

BEHAVIOR

When disturbed, hognosed snakes flatten their head and neck, spreading their vertebrae much like a cobra, owing to their nickname, "puff adder." This act gives the snake an almost impish grin when viewed from head-on. While spreading its "hood," the hognosed snake emits a loud hissing noise like steam escaping from kettle. Occasionally the bluffing snake will repeatedly strike at the would-be attacker but with its mouth closed. If the hissing, hooding and striking fail to dissuade the attacker, the hognosed snake will writhe with its mouth wide open, tongue lolling. Some snakes will eject blood from their lacrymal glands and emit musk from their cloaca. The belief is that a predator will instinctively ignore a dead animal that smells offensive. Of course, if the hognosed snake is righted, it will turn over on its back and again open its mouth.

CHARACTERISTICS

The Southern hognosed snake is thought to be most closely related to the Western hognosed snake; the two species being allopatric in their range distribution. Eckerman believes the development of the two species was influenced through geologic shifts and the subsequent isolation of the two species. Western hognosed snakes are most active in May when they begin breeding. Females lay their eggs in late spring or early summer. Typically hognosed snakes can be seen rooting through loose sand after toads during the early morning or late afternoon hours; although Western hognosed snakes feed primarily on amphibians, they are also known to feed on lizards and small mammals.

Eastern hognosed snakes become most active in May when they begin breeding. Females lay between four (4) and sixty (60) eggs in late spring or early summer.

FEEDING BEHAVIOR

According to studies conducted by numerous researchers and reported by Platt, throughout its range, amphibians made up 57% of the total diet while the rest consisted of reptiles and their eggs, birds, and mammals. Of the 57% of the amphibians consumed, approximately 88% were toads, representing only 50% of the total diet.

In another study, amphibians made up 44% of the total diet (toads made up only 22% of the total) while reptiles and mammals accounted for 39% and 33% respectively. Curiously, Ruthven also reported instances where western hognosed snakes attempted to eat ornate box turtles.

Among the food items eaten int he wild are fence and whiptail lizards, tiger and redback salamanders, and various species of frogs. Western hognosed snakes in captivity may feed exclusively on mice and small rodents. Initially, pinkie mice may have to be scented to encourage the neonate western hognosed snake.

As with other hognosed snakes, platirhinos uses its upturned snout to pursue amphibians as well as burrow into soft soil where it often resides. Although Platt states he has never observed Eastern Hognosed snakes digging up toads in the wild, his finding of large amounts of snad in the digestive tracts of hognosed snakes may relate to ingestion of prey items underground.

COMMENTS

Although Eastern hognosed snakes are sympatric throughout its range with both the Western hognosed snake and the Southern hognosed snake. There have few if any reports of Eastern hognosed snakes hybridizing with either of the two latter species; of those reports that exist, these are generally under captive conditions.

Although considered a G-5 species worldwide, the Western hognosed snake is rapidly being extirpated from much of its former range; this is due to a combination of factors including urbanization; habitat destruction and pollution; an increase in predation by feral dogs and cats, racoons and overcollection for export and domestic sale. It is considered a species of special concern or threatened locally. See the references below for more information

REFERENCES

Edgren (1952) Nat. Hist. Misc., Chicago Acad. Sci., No. 112, p. 3 Kennicott,R. (1860) Descriptions of new species of North American serpents in the museum of the Smithsonian Institution, Washington. PROC. ACAD. NAT. SCI. PHILADELPHIA 12: 328-338

Baird,S.F. and Girard,C. (1852) Characteristics of some new reptiles in the Museum of the Smithsonian Institution. PROC. ACAD. NAT. SCI. PHILADELPHIA 6: 68-70

Vazquesz-Diaz,J. et al. (1998) HERP. REV. 29 (3): 177

BIBLIOGRAPHY:

Blanchard, Frank A. 1939. A key to the Snakes of the United States, Canada and Lower California. Ann Arbor, University of Michigan Press.

Conant, Roger, and Joseph T. Collins. 1975 Reptiles and Amphibians of Eastern / Central North America. Houghton, Mifflin

Martoff, Bernard S., et al. Amphibians and Reptiles of the Carolinas and Virginia.1980. UNC Press. Chapel Hill, N.C.

Platt,D.R. (1969)
Natural History of the Hognose Snakes Heterodon platyrhinos and Heterodon nasicus.
University of Kansas, Museum of Natural History, vol 18, No. 4, pp. 253-420.