Neotropical sunbeam snakes

(Loxocemidae)

Class Reptilia

Order Squamata

Suborder Serpentes

Family Loxocemidae

Thumbnail description
A medium-sized snake with cylindrical, muscular body; small eyes with vertically elliptical pupils; small mouth; and short tail

Size
The maximum recorded total length is 5 ft (1.53 m), but most adults are less than 3 ft (1 m); the tail accounts for 10–14% of the snake's total length

Number of genera, species
1 genus, 1 species

Habitat
Tropical moist and dry forests, including coastal beaches

Conservation status
Not threatened

Distribution
Southwestern Mexico, Guatemala, Honduras, El Salvador, Nicaragua, and northwestern Costa Rica

Evolution and systematics

Loxocemus represents a lineage that probably arose independently and early in snake evolution. The genus was variously placed in the families Pythonidae (pythons), Boidae (boas and sand boas), or Xenopeltidae (Asian sunbeam snakes), but now systematists agree that it comprises a distinct family, Loxocemidae. Previously, some herpetologists recognized the form sumichrasti as either a distinct species or a subspecies of L. bicolor, but detailed studies of morphological and geographic variation demonstrated that no distinction between bicolor and sumichrasti is possible, and therefore a single, monotypic species is currently recognized, L. bicolor.

The taxonomy for this species is Loxocemus bicolor Cope, 1861, La Unión, San Salvador [El Salvador].

English common names for this species include Neotropical sunbeam snake, Mexican burrowing python, Mesoamerican python, New World python, ground python, and burrowing boa; Spanish common names include chatilla, pitón excavador, and boa excavadora.

Physical characteristics

Neotropical sunbeam snakes have a prominently upturned snout. The scales on top of the head are large, whereas the

scales on the body are smaller, smooth, and slightly iridescent. Pelvic spurs are present in both sexes but usually are not visible in females. Individuals are uniformly brown or have a white or cream belly sharply set off from the dark dorsum. In addition to this variation in body coloration, many individuals have small, highly irregular white blotches.

Distribution

This species is found in low and moderate elevations in southwestern Mexico, Guatemala, Honduras, El Salvador, Nicaragua, and northwestern Costa Rica.

Habitat

This species inhabits tropical moist and dry forests, including coastal beaches. Specimens have been found in banks of arroyos, rock piles, holes in the ground, under leaf litter and logs, behind the bark of logs, and inside ant nests.

Behavior

The species is relatively uncommon or infrequently seen throughout its distribution. As a result, its behavior in the wild is poorly known. The snakes are semifossorial, burrowing in loose soil or rotting foliage with their upturned snouts during the day and moving on the surface at night or on rainy days. Males engage in physical combat during the breeding season and can inflict severe wounds on their rivals by biting them.

Feeding ecology and diet

Loxocemus bicolor is a constrictor snake that forages widely for prey, relying on chemical and visual cues to locate prey outright or to restrict its attention to specific microhabitats.

Food items of three snakes from Mexico and one from Costa Rica included two whip-tailed lizards (Cnemidophorus sp.) and two small rodents. Costa Rican specimens also take eggs and hatchlings of black iguanas (Ctenosaura similis) and eggs of green iguanas (Iguana iguana) and olive ridley sea turtles (Lepidochelys olivacea). A 54 in (138 cm) (total body length) snake consumed 32 C. similis eggs, whereas a 55 in (140 cm) specimen ate 23 I. iguana and four C. similis eggs. Loxocemus apparently enters the nesting tunnels of lizards and sea turtles in search of eggs, which probably constitute seasonally important prey for the snake. Hatchlings are seized as they emerge from their nests. When feeding on sea turtle eggs, Loxocemus loops its body around the eggs before swallowing them whole; the coils are made with the venter toward the snake's head. In captivity, C. similis eggs are first bitten, pushed against the body with the mouth, and then ingested. Some eggs may be broken in the process, but most are swallowed intact.

Reproductive biology

The species is oviparous. One captive female laid four eggs, which averaged 3 in (78.8 mm) in length, 1.4 in (37 mm) in width, and 2.16 oz (61.5 g). In the wild, neonates are reportedly found in May and take four to five years to reach sexual maturity.

Conservation status

The species is not considered to be endangered or threatened but is listed on CITES Appendix II, which includes species whose trade must be controlled in order to avoid use that is incompatible with their survival.

Significance to humans

None known.

Resources

Books

Greene, H. W. Snakes: The Evolution of Mystery in Nature. Berkeley: University of California Press, 1997.

McDiarmid, R. W., J. A. Campbell, and T. Touré. Snake Species of the World. Vol. 1, A Taxonomic and Geographic Reference. Washington, DC: The Herpetologists' League, 1999.

Savage, J. M. The Amphibians and Reptiles of Costa Rica. Chicago: University of Chicago Press, 2002.

Wilson, L. D., and J. R. Meyer. The Snakes of Honduras, 2nd ed. Milwaukee: Milwaukee Public Museum, 1985.

Periodicals

Cundall, D., V. Wallach, and D. A. Rossman. "The Systematic Relationships of the Snake Genus Anomochilus." Zoological Journal of the Linnean Society 109 (1993): 275–299.

Greene, H. W. "Dietary Correlates of the Origin and Radiation of Snakes." American Zoologist 23 (1983): 431–441.

Mora, J. M. "Natural History Notes: Loxocemus bicolor (Burrowing Python). Feeding Behavior." Herpetological Review 22 (1991): 61.

——. "Predation by Loxocemus bicolor on the Eggs of Ctenosaura similis and Iguana iguana." Journal of Herpetology 21 (1987): 334–335.

Mora, J. M., and D. C. Robinson. "Predation of Sea Turtle Eggs (Lepidochelys) by the Snake Loxocemus bicolor Cope." Revista de Biología Tropical 32 (1984): 161–162.

Nelson, C. E., and J. R. Meyer. "Variation and Distribution of the Middle American Snake Genus, Loxocemus Cope (Boidae?)." Southwestern Naturalist 12 (1967): 439–453.

Odinchenko, V. I., and V. A. Latyshev. "Keeping and Breeding in Captivity the Mexican Burrowing Python Loxocemus bicolor (Cope, 1961) at Moscow Zoo." Russian Journal of Herpetology 3 (1996): 95–96.

Willard, D. E. "Constricting Methods of Snakes." Copeia 1977 (1977): 379–382.

Woodbury, A. M., and D. M. Woodbury. "Notes on Mexican Snakes from Oaxaca." Journal of the Washington Academy of Sciences 34 (1944): 360–373.

Other

"Convention on International Trade in Endangered Species of Wild Fauna and Flora." [cited September 24, 2002]. <http://www.cites.org>

Javier A. Rodríguez-Robles, PhD