Woodsnakes and spinejaw snakes

(Tropidophiidae)

Class Reptilia

Order Squamata

Suborder Serpentes

Family Tropidophiidae

Thumbnail description
Small constricting snakes possessing tracheal lung and without functional left lung; in most species males possess cloacal spurs and vestige of pelvic girdle

Size
4–41 in (10–106 cm); 1–16 oz (30–450 g)

Number of genera, species
5 genera; 25 species

Habitat
Open woodland, forest, cloud forest, palm groves, dry scrub forest, rocky hillsides, cliff faces, and caves

Conservation status
No species listed by IUCN

Distribution
Northwestern South America in Colombia and Ecuador; Amazonian Ecuador, Peru, and northwestern Brazil; southeastern Brazil; Central America; southern Mexico; West Indies; peninsular Malaysia and northern Borneo

Evolution and systematics

There are few snake fossils that can be incontrovertibly identified as woodsnakes. The fossil genus Boavus dating from the Eocene may belong to the Tropidophiidae. More recent fossils identified as Tropidophis are known from Pleistocene deposits in caves.

Woodsnakes are believed to have diverged from basal macrostomatan stock sometime after the divergence of the macrostomatans from alethinophidians at the end of the Cretaceous. Macrostomatan snakes are distinguished by characters of the skull and musculature that allow them increased jaw flexibility, a greater gape, and the ability to consume larger prey.

The woodsnakes are believed to have originated in northern South America and from there spread into Central America and the West Indies. The greatest diversity of woodsnakes exists in Cuba, where in the relative absence of other snakes the tropidophiid lineage became the dominant family of snakes on the large island. The origin and relationships of the two Asian species of spinejaw snakes in the genus Xenophidion are unclear at this time.

The phylogenetic relationship of the Tropidophiidae to other snake families is unclear. Traditionally, the sister taxon has been identified as the Boidae, but in recent years many authors have come to identify the Bolyeriidae as the most likely sister taxon.

As is typical of most macrostomatan snakes, most tropidophiid species have the vestiges of a pelvic girdle and cloacal spurs. However, in the Tropidophiidae, only male snakes have the vestigial pelvic girdle and cloacal spurs; Tropidophis semicinctus and both species of Xenophidion do not have the pelvic girdle and spurs.

Tropidophiid snakes do not have a functional left lung, as is characteristic of all caenophidian snakes. They do have a well-developed tracheal lung, a characteristic of many colubridoid snakes.

The Tropidophiidae has been well investigated and is relatively well-known. However, it is a widely distributed lineage that may be more speciose than is currently recognized. It seems likely that future phylogenetic analyses based on genetic characters will recognize some subspecies and some disjunct populations as new species. Two species, Tropidophis celiae and Tropidophis spiritus, were described as recently as 1999. The Asian genus Xenophidion was recognized in 1996, and tentatively placed in the Tropidophiidae in 2001.

Some authors recognize three distinct lineages within the Tropidophiidae, namely the Tropidophiinae comprised of the genera Tropidophis and Trachyboa; the Ungaliophiinae comprised of Ungaliophis and Exiliboa; and the Xenophidiinae with Xenophidion. It has been proposed that each of the three lineages should be recognized as a family. Future investigations will undoubtedly address and resolve the relationships of these genera.

Physical characteristics

The woodsnakes and spinejaw snakes are small, inoffensive, boa-like snakes. The bones of the lower jaw and the vestigial

pelvic girdle are similar to that of boas, while the absence of a functional left lung and the presence of a tracheal lung are more typical of colubrids. The hyoid apparatus and the condition of the contact between the prefrontal and internasal bones of the snout also are more similar to colubrids than boas.

The smallest woodsnake species is probably Tropidophis fuscus of Cuba; it is not known to exceed 12 in (30 cm). The largest species is Tropidophis melanurus of Cuba, with a reported maximum length of 41 in (106 cm).

Most woodsnakes and the spinejaw snakes are colored in shades of browns and grays, patterned with muted small blotches or stripes. There is a wide range of variation in the keels on dorsal scales in the genus Tropidophis; some species have individuals with smooth dorsal scales and others with strongly keeled dorsal scales. The incredibly rough, keeled, and spiky scalation of Trachyboa boulengeri makes it one of the most unusual snakes in the world.

Tropidophis feicki has the ability to change color to a slight degree, turning darker during the day and paler at night. The skin of several smooth-scaled taxa of woodsnakes exhibits iridescence; the large flat scales of Exiliboa placata are both shiny and iridescent, while the smaller ruggedly keeled scales of Trachyboa gularis give a drab and dusty appearance.

Distribution

The Tropidophiidae is distributed from southeastern Brazil to southern Mexico and the West Indies. The genus Tropidophis is the most widespread, with three species found in South America and 15 species in the West Indies. The genus Trachyboa occurs from the Choco region of Panama south into Ecuador. Ungaliophis is found from the state of Chiapas in southern Mexico south to the Pacific coast of Colombia. Exiliboa is known only from two mountain ranges in Oaxaca, Mexico. Xenophidion is known from peninsular Malaysia and northern Borneo.

Habitat

Woodsnakes can be found in a variety of habitats, including open woodlands, forest, cloud forest, dry scrub forest, rocky slopes, rainforests, palm groves, agricultural areas, caves, and cliffs. Woodsnakes in general are mesophilic in their habitat preferences, avoiding extremes and existing in environments that are neither too wet nor too dry.

Most tropidophiid species are found at lower elevations from sea level to 2,000 ft (less than 600 m). Two species are found at high elevation: Exiliboa placata is found at elevations of 7,500 ft (2,300 m) and Tropidophis taczanowskyi occurs in the northern Andes at elevations of 6,500–10,000 ft (2,000–3,000 m).

Behavior

Woodsnakes tend to be nocturnal, but they are often encountered moving or basking during the day. Faced with a perceived threat, most woodsnakes meekly coil into a ball; Trachyboa coils into a flat disk with its head in the center. If physically molested, a woodsnake may release odiferous anal secretions. It is rare that any woodsnake bites in defense. Several species of Tropidophis are reported to autohemorrhage, spontaneously bleeding from the mouth, nostrils, and eyes when severely stressed.

Most tropidophiid snakes are terrestrial, but many are occasionally observed to climb into bushes, vines, and low trees. The bromeliad woodsnakes, Ungaliophis panamensis and Ungaliophis continentalis, are probably the most arboreal of the woodsnakes; both species are known to live high in trees, burrowing in the epiphytic growth on large limbs; U. panamensis has been accidentally shipped to Europe and the United States in bunches of bananas. Tropidophis paucisquamis also has been observed climbing in vegetation 3–10 ft (1–3 m) above the ground.

Feeding ecology and diet

The feeding behavior of woodsnakes is not well known. They have been observed actively foraging, and it is likely that

they also incorporate ambush techniques. Anoline lizards comprise a large percentage of the diet of West Indian Tropidophis species. Most woodsnakes will accept eleutherodactylid frogs as prey; in captivity, E. placata readily accepts small eleutherodactylid frogs as prey, but refuses similar-sized hylid and ranid frogs. Small salamanders and frog eggs have been found in the stomachs of wild Exiliboa. Both Trachyboa species feed on fishes and amphibians. Large individuals of T. melanurus are known to feed on small mammals and birds. Larger adult specimens of many species of Tropidophis and both species of Ungaliophis are known to accept newborn mice in captivity.

Reproductive biology

All woodsnakes bear live young.

Conservation status

No species of Tropidophiidae is listed on the 2002 IUCN Red List. In the 1990s, the Navassa woodsnake, Tropidophis bucculentus, was reported as likely extinct. Habitat disturbance and mongoose predation are reported to be significant factors in the demise of this species.

Little is known about the status of any woodsnake species in the wild. No base-line population density studies are published.

Significance to humans

Woodsnakes in nature exist largely unseen and unbothered by humans. Some species are kept and bred in captivity.

Species accounts

List of Species

Banded woodsnake

Tropidophis feicki

taxonomy

Tropidophis feicki Schwartz, 1957, Cuéva de los Índios, San Vícente, Pínar del Río Province, Cuba.

other common names

English: Banded dwarf boa, Feick's dwarf boa; French: Boa forestier de Feick; Spanish: Majá.

physical characteristics

This is a medium-sized woodsnake with a reported maximum length of 20 in (50.5 cm). The head of this slender snake is distinctly wider than the neck. Banded woodsnakes are boldly marked with 17–26 dark bands on the body. They are smooth-scaled, shiny, and iridescent.

distribution

This species is found in the western third of Cuba.

habitat

The banded woodsnake is associated with wooded areas. It has been collected on cliff faces and in caves, as well. While the

species is considered to be predominantly terrestrial, specimens have been found climbing in trees and vines.

behavior

Like most woodsnakes, the banded woodsnake is a calm and docile snake that coils into a ball when threatened. This beautiful snake tends to be slow and deliberate in its movements.

feeding ecology and diet

The banded woodsnake feeds primarily on anoline lizards. It is reported that in captivity all ages accept appropriately sized Anolis carolinensis as suitable prey. Large adults will feed on pink mice in captivity.

reproductive biology

This species is viviparous. Little is known about its reproduction in nature.

The San Antonio Zoo reported on the birth of two litters of T. feicki, both born in September 1999. The eight neonates ranged in length from 5.6 in to 7.3 in (14.4 cm to 18.5 cm) and in weight from 0.07 oz to 0.12 oz (2.1g to 3.5 g). Prior to breeding, the two pairs of adult parents were subjected to both daily and seasonal temperature fluctuations. Throughout most of the year, temperatures were kept fairly constant, varying only 78–80°F (26–27°C); from December through February the daily temperatures varied from 62.6°F to 80.6°F (17°C to 27°C).

conservation status

Nothing is known about the numbers in the wild.

significance to humans

The banded woodsnake exists in nature largely unseen and unmolested by humans. It is one of the most attractive species of woodsnakes, but few specimens have come from Cuba and the species is rarely seen in captivity.

Southern bromeliad woodsnake

Ungaliophis panamensis

taxonomy

Ungaliophis panamensis Schmidt, 1933, Cérro Brujo, Colón Province, Panamá.

other common names

English: Bromeliad boa, bromeliad dwarf boa, banana boa; French: Boa nain; German: Bananenboa; Spanish: Boa enana.

physical characteristics

This is a medium-sized woodsnake with a reported maximum length approaching 30 in (76 cm). This is a slender, smooth-scaled snake, pale gray or tan with a distinct pattern of black triangular blotches on the back. There is a single large prefrontal scale, the scale on top of the snout; this character distinguishes this genus from other tropidophiids. Females do not have cloacal spurs, but males have prominent large spurs.

distribution

The southern bromeliad woodsnake occurs at low to moderate elevations in southeastern Nicaragua, Costa Rica, Panama, and western Colombia.

habitat

Southern bromeliad woodsnakes are associated with primary and secondary forest. The species has been encountered on the ground and has been collected in the verdant epiphytic growth of large trees when they are felled.

behavior

This is a very pleasant snake to handle, being inoffensive by nature and deliberate and docile in actions. The southern bromeliad woodsnake does not bite in defense. When threatened or molested, it coils into a ball. Only rarely does this species discharge its odiferous anal secretions when molested.

feeding ecology and diet

In nature, it is believed that this species feeds primarily on small lizards and frogs. In captivity, all ages will usually accept appropriately sized Anolis sagrei and Anolis carolinensis lizards as prey; adults usually feed on appropriately sized rodents.

reproductive biology

This species is viviparous. Very little is known about the reproduction of this species in nature or captivity. Neonates are about 6 in (15 cm) in length.

conservation status

Nothing is known about the numbers in the wild.

significance to humans

This species is rarely kept in captivity. In nature the southern bromeliad woodsnake is rarely observed. The species is largely unseen and unmolested by humans.

Resources

Books

Crother, Brian I., ed. Caribbean Amphibians and Reptiles. San Diego: Academic Press, 1999.

Duellman, William E., ed. The South American Herpetofauna: Its Origin, Evolution and Dispersal. Monograph of the Museum of Natural History, Number 7. Lawrence: The University of Kansas, 1979.

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

McDiarmid, Roy W., Jonathan A. Campbell, and T'Shaka A. Touré. Snake Species of the World. Washington, DC: The Herpetologists' League, 1999.

Schwartz, Albert, and Robert W. Henderson. Amphibians and Reptiles of the West Indies. Gainesville: University of Florida Press, 1991.

Tolson, P. J., and R. W. Henderson. The Natural History of West Indian Boas. Taunton: R & A Publishing Limited, 1993.

Zug, G. R., L. J. Vitt, and J. P. Caldwell. Herpetology. 2nd ed. San Diego: Academic Press, 2001.

Periodicals

Barbour, Thomas, and Charles T. Ramsden. "The Herpetology of Cuba." Memoirs of the Museum of Comparative Zoology XLVII, no. 2 (May 1919): 1–213 plus 15 plates.

Bogert, Charles M. "Variations and Affinities of the Dwarf Boas of the Genus Ungaliophis." American Museum Novitates no. 2340 (August 9, 1968): 1–26.

——. "A New Genus and Species of Dwarf Boa from Southern Mexico." American Museum Novitates no. 2354 (December 18, 1968): 1–38.

Burger, R. Michael. "The Arboreal Burrower: The Dwarf Boa Ungaliophis." Vivarium 7, no. 2 (June 1998): 46–49.

——. "Observations on Courtship Behavior in Ungaliophis Mueller." Bulletin of the Chicago Herpetological Society 31, no. 4 (April 1996): 57–59.

——. "The Bromeliad Boa (Ungaliophis continentalis)." Reptiles 6, no. 6 (June 1998): 12–14.

McDowell, S. B. "A Catalogue of the Snakes of New Guinea and the Solomons, with Special Reference to Those in the Bernice P. Bishop Museum. Part 2. Anilioidae and Pythoninae." Journal of Herpetology 9, no. 1 (1975): 1–80.

Schwartz, Albert. "A New Species of Boa (genus Tropidophis) from Western Cuba." American Museum Novitates, no. 1839 (August 19, 1957): 1–8.

Schwartz, Albert, and Robert J. Marsh. "A Review of the Pardalis-maculatus Complex of the Boid Genus Tropidophis of the West Indies." Bulletin of the Museum of Comparative Zoology 123, no. 2 (1960): 49–89.

Stull, Olive Griffith. "A Revision of the Genus Tropidophis." Occasional Papers of the Museum of Zoology, no. 135 (October 1, 1928): 1–51.

Wallach, V., and R. Günther. "Visceral Anatomy of the Malaysian Snake Genus Xenophidion, Including a Cladistic Analysis and Allocation to a New Fmaily." Amphibia Reptilia 19, no. 4 (1998): 385–404.

Wilcox, T. P., Derrick J. Zwickl, Tracy A. Heath, and David M. Hillis. "Phylogenetic Relationships of the Dwarf Boas and a Comparison of Bayesian and Bootstrap Measures of Phylogenetic Support." Molecular Phylogenetics and Evolution 25, no. 2 (2002): 361–371.

David G. Barker, MS

Tracy M. Barker, MS