Slender blindsnakes

(Leptotyphlopidae)

Class Reptilia

Order Squamata

Suborder Serpentes

Family Leptotyphlopidae

Thumbnail description
Small, slender, fossorial snakes with smooth, uniformly sized body scales, highly reduced eyes, a small, ventrally placed mouth, rounded or hook-shaped snout, and short tail bearing a sharp terminal spine

Size
2.3–15.3 in (5.8–38.9 cm)

Number of genera, species
2 genera; 93 species

Habitat
Soil

Conservation status
Not classified by the IUCN

Distribution
Africa, southwest Asia, southern North America, Central America, the West Indies, and South America

Evolution and systematics

Most recent phylogenetic analyses have placed Leptotyphlopidae together with Anomalepididae (early blindsnakes) and Typhlopidae (blindsnakes) in Scolecophidia, one of two infraorders recognized within Serpentes (the clade that includes all living snakes). However, the interrelationships among the three groups of blindsnakes are poorly understood. The unusual form and position of the hyoid in Leptotyphlopidae and Typhlopidae are suggestive of a close relationship between these two families. However, similarities in skull structure, visceral anatomy, and scalation patterns suggest that Anomalepididae and Typhlopidae are more closely related to each other than either is to Leptotyphlopidae. Unfortunately, the fossil record for Leptotyphlopidae is exceptionally poor, and the few fossil remains that are known offer little insight into the evolutionary history of the family. Interrelationships within Leptotyphlopidae are also poorly known. Nearly 20 species groups are tentatively recognized, but there have been no large-scale phylogenetic analyses that have addressed interspecific relationships within the family.

No subfamilies are recognized.

Physical characteristics

The family Leptotyphlopidae includes the most highly miniaturized snakes in the world. Although a few species (e.g., Leptotyphlops humilis, L. melanotermus, L. occidentalis, L. tricolor, L. weyrauchi, and Rhinoleptus koniagui) occasionally grow to lengths of over 1 ft (30 cm), most forms are significantly smaller, ranging between 4 and 10 in (10 and 25 cm) in total length and often weighing less than 0.05 oz (1.4 g). Even more remarkable than their short length, however, is their extremely narrow build, a characteristic reflected in their common names, "slender blindsnakes," "threadsnakes," and "wormsnakes." Most species attain a maximum body width of only 0.04–0.20 in (0.1–0.5 cm) and exhibit aspect ratios (total length divided by body width) of between 40 and 100. Two exceptionally slender species, L. macrorhynchus and L. occidentalis, occasionally have aspect ratios exceeding 140, and even the stoutest forms (e.g., L. broadleyi and L. boulengeri) are more slender than most other snakes, rarely having aspect ratios of less than 30.

Leptotyphlopids bear a strong superficial resemblance to other blindsnakes (Anomalepididae and Typhlopidae) in having cylindrical bodies covered by smooth, equally sized, cycloid scales, short lower jaws countersunk into the ventral surface of the head, and vestigial eyes that are scarcely visible beneath the enlarged head scales. (However, in some species, most notably Leptotyphlops macrops, the eyes are larger and more highly developed.) In addition, all forms have numerous tactile organs housed within the anterior head scales, often visible to the naked eye as tiny, light-colored specks on the external surfaces of the scales. However, several morphological characteristics serve to distinguish leptotyphlopids from anomalepidid and typhlopid blindsnakes. In particular, all slender blindsnakes have either 14 (in Leptotyphlops) or 16 (in Rhinoleptus) rows of scales encircling the body (all anomalepidids and nearly all typhlopids have more than 16 scale rows), a single anal shield (all anomalepidids and nearly all typhlopids have two or more), and a distinctive arrangement of the scales along the upper lip. Moreover, leptotyphlopids are unique among snakes in having teeth only on the lower jaw.

Slender blindsnakes are generally rather dull in appearance. Although a few South American species (e.g., Leptotyphlops

alfredschmidti, L. teaguei, L. tricolor) are boldly patterned with multicolored dorsal stripes, most leptotyphlopids are patternless and have a relatively uniform pink, gray, tan, brown, or black dorsal coloration. Those forms that are pinkish in color, such as the two species found in the southwestern United States (L. dulcis and L. humilis), bear an uncanny superficial resemblance to earthworms, thus giving rise to another common name for these diminutive serpents, "wormsnakes."

The size and shape of both the snout and tail are somewhat variable within Leptotyphlopidae. Most species of Leptotyphlops have relatively blunt, rounded snouts. However, several Old World species (e.g., L. macrorhynchus, L. parkeri, L. rostratus) have prominent, hook-shaped snouts, and in two Socotran forms (L. filiformis and L. macrurus), the snout is both hooked and pointed. A pointed snout is also seen in Rhinoleptus koniagui. Such highly derived snout morphologies are less common among New World taxa, but they are seen in a few South American species (e.g., L. borrichianus and L. unguirostris). As in most other blindsnakes, the scales surrounding the snout in leptotyphlopids are somewhat larger than those surrounding the body, and in at least one species (L. humilis), the largest of these scales (the rostral) fluoresces under ultraviolet light. In most taxa, the tail constitutes 5–10% of the snake's total length, but this figure may be as low as 2.1% in short-tailed species (e.g., L. septemstriatus), or as high as 18.9% in long-tailed species (e.g., L. macrurus and L. wilsoni). The tail usually terminates in a small needle- or thorn-shaped apical spine.

Leptotyphlopids are also characterized by a number of distinctive internal anatomical features. The most significant of these relate to the structure of the jaws. The upper jaws are toothless and relatively immobile. In contrast, the lower jaw bears teeth and is highly flexible due to the presence of exceptionally well-developed intramandibular joints, which divide the left and right halves of the lower jaw into separate anterior and posterior segments. Also unusual are the form and position of the hyoid apparatus, which is Y-shaped and located far behind the head (characteristics also seen in typhlopid blindsnakes). The pelvic apparatus is, in general, more complete than that of other snakes, typically consisting of paired ilia, ischia, pubes, and femora (although in some taxa the pelvis is highly reduced [e.g., Leptotyphlops macrorhynchus] or absent [e.g., L. cairi]). Even in species that possess well-developed femora, however, the horny spurs on the distal ends of the femora rarely protrude through the skin as they commonly do in other basal snakes (e.g., pipesnakes, boas, pythons). Perhaps the most bizarre osteological feature of Leptotyphlopidae is seen in several Old World species of Leptotyphlops (e.g., L. cairi, L. macrorhynchus, L. nursii, and L. occidentalis), in which much of the skull roof has been lost.

Distribution

Slender blindsnakes have a relatively wide geographical distribution, ranging throughout the Ethiopian and Neotropical regions and extending northward into southern portions of the Palearctic and Nearctic regions as well. All but one of the approximately 93 species of Leptotyphlopidae are contained in the genus Leptotyphlops. In the Old World, this genus is distributed throughout Africa and the Arabian Peninsula, with two species (L. blanfordi and L. macrorhynchus) extending eastward as far as northwestern India. Also, three species (L. filiformis, L. macrurus, and L. wilsoni) are endemic to the island of Socotra in the northwestern Indian Ocean, and a small number of mainland species are known to inhabit several islands off the coast of Africa (e.g., Pemba and Bioco). In the New World, Leptotyphlops ranges throughout most of South America (excluding Chile, southern Argentina, and southern Peru) and all of Central America and Mexico, with two species (L. dulcis and L. humilis) extending northward into the southwestern United States. In addition, six species are endemic to islands of the West Indies, and several mainland species are known from islands along the coasts of Mexico and Central America. The numbers of Old World and New World species of Leptotyphlops are approximately equal. The genus Rhinoleptus includes only a single species, R. koniagui, which is known from Guinea and Senegal in western Africa. The altitudinal distribution of slender blindsnakes is remarkable given the extraordinarily small size of these ectothermic animals. They have been found at elevations ranging from 250 ft (76 m) below sea level (L. humilis in Death Valley, California) to 10,660 ft (3,250 m) above sea level (L. tricolor in the Peruvian Andes).

Habitat

Slender blindsnakes are known to occur in a relatively broad array of habitats, including deserts, tropical rainforests, dry woodlands, savannas, plantations, and boulder-strewn mountain slopes. Throughout these many macrohabitats, however, they are generally found within a relatively narrow range of microhabitats. They are most frequently found in shallow soil, amidst leaf litter and other surface debris, or beneath stones or logs. They are also occasionally encountered within rotten logs, anthills, and termite nests. The strong preference that these tiny snakes appear to have for such microhabitats is likely related at least in part to their extremely high surface-to-volume ratios, which make the crucial tasks of regulating body temperature and minimizing evaporative water loss especially challenging. Laboratory experiments on captive animals suggest that the hydric environment is especially important to these fossorial snakes. When placed in enclosures containing soils of different moisture levels, they avoid the drier soils, choosing instead to seek out microenvironments having higher moisture levels. One form, Leptotyphlops natatrix, may even be semiaquatic or aquatic. This species, known only from the type specimen collected in Gambia in 1931, has a laterally compressed, oarlike tail (like those seen in sea snakes) and was found in a swamp. Several species of Leptotyphlops have also been found climbing trees. It is unclear, however, whether arboreality is common among these snakes, or if they merely occasionally pursue their prey (mainly ants and termites) into trees.

Behavior

Leptotyphlopids are predominantly fossorial snakes. They are most commonly encountered by humans either during the course of digging operations (in some cases as far as 49 ft [15 m] beneath the surface) or after heavy rains have flooded them out of their subterranean retreats. No observations have been made on their burrowing behavior, but it is likely that they make extensive use of preexisting animal burrows and root systems when moving about underground. They can quickly burrow into loose soils such as sand, but they appear to lack the strength necessary to construct their own tunnels in compact soils.

Although these secretive snakes spend most of their lives underground, they do occasionally venture above ground during the evening hours to search for food or mates. When disturbed by potential predators during these above-ground excursions, they immediately attempt to escape into the ground. If this fails, however, they have several additional defensive strategies that they may implement. When restrained, they usually thrash about violently in an attempt to escape. If a snake cannot wiggle free from danger, it will jab its captor with its sharp tail spine and void the contents of its cloaca. As a last resort, some species will become rigid and fake death.

Feeding ecology and diet

Slender blindsnakes feed exclusively on small invertebrate prey. Some species consume a relatively wide variety of such animals, including beetles, caterpillars, centipedes, cockroaches, crickets, fly larvae, harvestmen, millipedes, and spiders. However, the bulk of their diet consists mainly of ant brood and termites. Like other snakes, they rely heavily on chemoreception to find their prey. They are able to follow the pheromone trails of ants and termites with relative ease, allowing them to locate large colonies of these abundant social insects in almost any environment. Once the snakes enter these colonies, they go into a feeding frenzy and quickly gorge themselves, often eating hundreds of prey items in a single meal. They ingest their prey using a unique feeding mechanism, in which the front half of the lower jaw is rapidly flexed in and out of the mouth to ratchet prey into the throat. This mandibular raking mechanism allows leptotyphlopids to feed very rapidly, thereby minimizing the time that they are exposed to the attacks of ants and termites defending their nests.

These tiny snakes also have evolved an elaborate defensive behavior to help protect themselves from the bites and stings of ants. When molested, they briefly retreat from their attackers and coil into a ball. They then expel a mixture of glandular secretions and feces from the cloaca and begin to writhe within their coils, deliberately spreading this mixture over their entire bodies. After several minutes of this, the snakes take on a glossy, silvery appearance. More importantly, however, they emerge from their coils with at least a partial immunity to ant attacks. The secret to this defensive strategy is a mixture of chemicals in the snakes' cloacal secretions that has a strong repellent effect on ants. Once the snakes have applied this "ant repellent," they resume feeding, during which time they are generally left unbothered by the ants.

Reproductive biology

The reproductive biology of slender blindsnakes is poorly known. All species are believed to be oviparous, but detailed data are available only for two South African species (Leptotyphlops conjunctus and L. scutifrons) and two North American species (L. dulcis and L. humilis). In these subtropical forms, reproduction is highly seasonal, with courtship and mating occurring in the spring and oviposition occurring in the summer. Clutch size typically ranges between two and seven eggs. However, some species occasionally deposit clutches consisting of only a single egg, and one Latin American species (L. goudotii) is known to produce clutches of up to 12 eggs. The elongate, thin-shelled eggs are generally 0.6–1 in (1.5–2.5 cm) in length, but measure only 0.08–0.16 in (0.2–0.4 cm) in width. Natural incubation times are unknown, but one clutch of L. humilis eggs incubated in captivity at 86°F (30°C) hatched after 94 days. Hatchling size appears to vary widely between species, ranging from less than 2.4 in (6.1 cm) in some small species to over 4.3 in (11 cm) in larger species.

Conservation status

No species are listed by the IUCN.

Significance to humans

Because of their extremely small size and secretive nature, slender blindsnakes are of no economic significance to humans. However, in areas where they are particularly abundant, they may benefit humans by keeping populations of ants and termites in check.

Species accounts

List of Species

Texas blindsnake

Leptotyphlops dulcis

taxonomy

Leptotyphlops dulcis (Baird and Girard, 1853), between San Pedro and Camanche [Comanche] Springs, Texas. Five sub-species are recognized.

other common names

English: Texas threadsnake, Texas wormsnake; French: Leptotyphlops du Texas; German: Texas-Schlankblindschlange; Spanish: Serpiente-lombriz texana.

physical characteristics

2.6–10.7 in (6.6–27 cm) in total length. Tail 5–6% of total length. Midbody diameter 0.06–0.22 in (0.15–0.5 cm). Adult aspect ratio of approximately 50. Pink or reddish brown dorsally, light pink or cream-colored ventrally.

distribution

Southwestern United States (southern Kansas, central and western Oklahoma, central and western Texas, southern New Mexico, and southeastern Arizona) and northeastern Mexico (northeastern Sonora, northeastern Chihuahua, Coahuila,

Nuevo Leon, Tamaulipas, northern Veracruz, San Luis Potosi, and northern Zacatecas).

habitat

These snakes inhabit deserts, grassy plains, oak and juniper woodlands, and rock-strewn mountain slopes. They are usually found buried in sandy or loamy soil, or beneath stones, logs, or other surface debris, often near some source of water.

behavior

Texas blindsnakes are predominantly fossorial. However, they are occasionally encountered above ground at night or after heavy rains. They move somewhat clumsily above ground, using a combination of undulatory, rectilinear, and concertina locomotion. In the case of the latter, the tail spine may be used as an anchor point.

feeding ecology and diet

These snakes feed mainly on ant brood and termites. They swallow ant larvae and pupae whole, but their prey-handling strategies vary when they feed on termites. They always attack termites from behind and sometimes swallow them whole. In some cases, they ingest only the abdomen and thorax and break off the head. In still other instances, the snakes merely chew on the termites, draining their abdominal fluids. Less common prey include ant lions, beetles, caterpillars, cockroaches, earwigs, fly larvae, and spiders. Texas blindsnakes are sometimes observed foraging amidst raiding columns of army ants. Eastern screech owls (Otus asio) often capture these snakes alive and bring them back to their nests, where the snakes feed on parasitic invertebrates amidst the nest debris.

reproductive biology

Courtship and mating occur throughout the spring and often involve aggregations of more than a dozen individuals. Oviposition usually occurs in June or July. Clutch size ranges between two and seven eggs, each measuring approximately 0.59 by 0.16 in (1.5 by 0.4 cm). Following oviposition, females coil around their eggs, in some cases in close proximity to other brooding females. Hatchlings, measuring 2.6–3 in (6.6–7.6 cm) in length, emerge in late summer.

conservation status

Not threatened.

significance to humans

None known.

Peters' wormsnake

Leptotyphlops scutifrons

taxonomy

Leptotyphlops scutifrons (Peters, 1854), Sena [Mozambique]. Two subspecies are recognized.

other common names

English: Peters' threadsnake, Peters' earthsnake, shielded blindsnake, scaly-fronted wormsnake, glossy wormsnake; German: Glanzende Schlankblindschlange.

physical characteristics

2.8–11 in (7–28 cm) in total length. Tail 5–13% of total length. Midbody diameter 0.06–0.16 in (0.15–0.4 cm). Aspect ratio between 40 and 89. Black, dark brown, or reddish brown dorsally (often with pale-edged scales), paler ventrally.

distribution

Southern Africa (Republic of South Africa, Swaziland, Namibia, Botswana, Zimbabwe, Mozambique, Angola, Zambia, Malawi, Tanzania, Kenya).

habitat

These snakes inhabit mainly savannas, where they are found in soil or beneath stones, logs, and other surface debris.

behavior

Peters' wormsnakes are fossorial. They are most frequently found above ground at night after heavy rains.

feeding ecology and diet

These snakes feed mainly on the eggs, larvae, and pupae of ants, and occasionally eat termites.

reproductive biology

Mating takes place in the spring. Oviposition occurs in the early summer (usually December or January). The eggs, measuring between 0.51 and 0.99 in (1.3–2.5 cm) in length and between 0.09 and 0.16 in (0.2–0.4 cm) in width, are usually deposited in clutches of one to three, although clutches of up to seven eggs have been reported. The elongate eggs are linked together like a string of sausages. The hatchlings, measuring 2.8 in (7.1 cm) or less in length, appear to emerge in late summer or early autumn (February or March).

conservation status

Not threatened.

significance to humans

None known.

Resources

Books

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

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

Shaw, C. E., and S. Campbell. Snakes of the American West. New York: Alfred A. Knopf, 1974.

Werler, J. E., and J. R. Dixon. Texas Snakes: Identification, Distribution, and Natural History. Austin: University of Texas Press, 2000.

Periodicals

Beebe, W. "Field Notes on the Snakes of Kartabo, British Guiana, and Caripito, Venezuela." Zoologica 31 (1946): 11–52.

Brattstrom, B. H., and R. C. Schwenkmeyer. "Notes on the Natural History of the Worm Snake, Leptotyphlops humilis." Herpetologica 7 (1951): 193–196.

Broadley, D. G., and S. Broadley. "A Review of the African Worm Snakes from South of Latitude 12°S (Serpentes: Leptotyphlopidae)." Syntarsus 5 (1999): 1–36.

Gehlbach, F. R., and R. S. Baldridge. "Live Blind Snakes (Leptotyphlops dulcis) in Eastern Screech Owl (Otus asio) Nests: A Novel Commensalism." Oecologica 71 (1987): 560–563.

Hahn, D. E., and V. Wallach. "Comments on the Systematics of Old World Leptotyphlops (Serpentes: Leptotyphlopidae), with Description of a New Species." Hamadryad 23 (1998): 50–62.

Hoogmoed, M. S. "On a New Species of Leptotyphlops from Surinam, with Notes on the Other Surinam Species of the Genus (Leptotyphlopidae, Serpentes). Notes on the Herpetofauna of Surinam V." Zoologische Mededelingen 51 (1977): 99–123.

Klauber, L. M. "The Worm Snakes of the Genus Leptotyphlops in the United States and Northern Mexico." Transactions of the San Diego Society of Natural History 9 (1940): 87–162.

Kley, N. J., and E. L. Brainerd. "Feeding by Mandibular Raking in a Snake." Nature 402 (1999): 369–370.

List, J. C. "Comparative Osteology of the Snake Families Typhlopidae and Leptotyphlopidae." Illinois Biological Monographs 36 (1966): 1–112.

Watkins II, J. F., F. R. Gehlbach, and J. C. Kroll. "Attractant-Repellent Secretions of Blind Snakes (Leptotyphlops dulcis) and their Army Ant Prey (Neivamyrmex nigrescens)." Ecology 50 (1969): 1,098–1,102.

Webb, J. K., R. Shine, W. R. Branch, and P. S. Harlow. "Life-History Strategies in Basal Snakes: Reproduction and Dietary Habits of the African Thread Snake Leptotyphlops scutifrons (Serpentes: Leptotyphlopidae)." Journal of Zoology, London 250 (2000): 321–327.

Nathan J. Kley, PhD