Mexican Hognosed Snake (Heterodon n kennerlyi)

SPECIES: H. n. kennerlyiKennicott, 1860 Mexican Hognose Snake

COMMON NAME:

Mexican Hognose Snake

FAMILY:

Colubridae

DISTRIBUTION:

Heterodon n. kennerlyi ranges from extreme southern Texas to southeastern Arizona south to northern Zacatecas, San Luis Potosi, and Aguascalientes, Mexico.

HABITAT:

Mexican 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.

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 less than 32 (males) to 37 (females) dorsal blotches of a grayish brown, deep cinnamon, or chocolate brown occur on the dorsum and alternate with rows of 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 six 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 hognose 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 hognose 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 hognose is righted, it will turn over on its back and again open its mouth. Western hognosed ssnakes are less likely to perform the entire act as are Easterns; however, neonate Mexican hognosed snakes may perform this ritual in captivity until they have become used to their keeper's actions.

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. Mexican hognosed snakes are most active in May when they begin breeding. Females lay their eggs in late spring or early summer. Typically Mexican hognosedn snakes can be seen rooting through loose sand after toads and lizard eggs during the early morning or late afternoon hours; although Mexican hognosed snakes feed primarily on amphibians, they are also known to feed on lizards and small mammals.

FEEDING BEHAVIOR

Among the food items eaten in the wild are fence and whiptail lizards and their eggs, salamanders, various species of frogs and tadpoles. Mexican hognosed snakes in captivity may be fed exclusively on mice and small rodents. Initially, pinkie mice may have to be scented to encourage the neonate western hognosed snake, but eventually they will take unscented mice. There are also reports of captive snakes eating the commercial snake sausages.

As with other hognosed snakes, kennerlyi uses its upturned snout to pursue amphibians as well as burrow into soft soil where it often resides. In Arizona, kennerlyi can be observed hunting asphalt and sandy roads during rainstorms in search of scaphiopus and salamanders.

STATUS

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.