African Burrowing Snakes (Atractaspididae)

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African burrowing snakes

(Atractaspididae)

Class Reptilia

Order Squamata

Suborder Serpentes

Family Atractaspididae

Thumbnail description
These snakes have small heads, smooth scales without apical pits, small to minute eyes with round pupils, and no loreal scale; one group, burrowing asps (Atractaspis), has unusual erectile front fangs

Size
12–40 in (30–102 cm)

Number of genera, species
12 genera; 62 species

Habitat
Forest, savanna, and near desert

Conservation status
Not threatened

Distribution
Sub-Saharan Africa, with one genus entering the Near East

Evolution and systematics

These unique snakes have caused great taxonomic confusion. Early classifications placed undue emphasis on the presence of erectile front fangs in burrowing asps. Due to this sole feature, for many years they were called mole vipers or burrowing adders and mistakenly were placed in the family Viperidae, even though they did not look like other vipers. It is now known that the fang erection mechanism of burrowing asps is unique and unlike that of true vipers.

Burrowing asps look very similar to and have similar lifestyles to other African burrowers, including the exotic-sounding purple-glossed snakes (Amblyodipsas), quill-snouted snakes (Xenocalamus), and centipede eaters (Aparallactus). They are now placed together, although confusion remains over the relationships and status of some genera within the family. Many have been combined into the snake eaters (Polemon), while at least one other genus (Elapotinus) is known from only a single specimen that may not even be African. The affinities of African burrowing snakes with other snakes also remain obscure. They share some intriguing similarities with primitive elapid snakes, e.g., the harlequin snakes (Homoroselaps) from South Africa, and may be close to the basal stock from which the important and venomous elapid snakes arose.

Two subfamilies are recognized. The Aparallactinae contains 11 genera, 25 species, of small- to medium-sized burrowers that are mainly back-fanged. The Atractaspidinae contains only a single genus (Atractaspis) with 17 species, distinguished by its unusual method of fang erection.

Physical characteristics

A wide range of fang types and associated glands is found in these unusual burrowing snakes. They all have similar skulls, vertebrae, and hemipenes. They are usually back-fanged, but one genus has long, hollow fangs that can rotate forward and inject venom. The small head is not distinct from the neck, and the snout is usually bluntly rounded (but very pointed in quill-snouted snakes, Xenocalamus). To aid in burrowing, the head shields often fuse and are thus reduced in number. The body is cylindrical and sometimes very long and thin. Many of these snakes are uniform black or brown, often with a light or dark collar. A few species are brightly striped, but blotched patterns are rare.

Distribution

Restricted to sub-Saharan Africa, with the small-scaled burrowing asps (Atractaspis microlepidota) extending into Israel and another (Micrelaps muelleri) into Jordan.

Habitat

Most species burrow in sand soils in savannas or desert scrublands. Others live in moist, humid soils of lowland forests.

Behavior

All live underground, some utilizing existing animal tunnels and others pushing through loose sand or leaf litter. Most species are gentle in the hand, but burrowing asps are irascible (easily provoked) and strike quickly and often. Only one fang is used and the mouth remains closed. The straight, thin fang protrudes from the side of the mouth and is hooked side-ways and backwards into the prey or victim. This unusual behavior has led to another common name, the side-stabbing snake. They may also be called stiletto snakes. Unlike other venomous snakes, they cannot be safely held behind the head.

Yellow and black burrowing snakes (Chilorhinophis) have blunt, tiny tails that mimic the head color. When disturbed by a predator, it hides its head beneath body coils and slowly waves the raised tail to deflect attack away from the delicate head.

Feeding ecology and diet

Most species eat other burrowing reptiles, including blind-snakes, wormlizards, or legless lizards. Others have more specialized diets. As their name implies, centipede eaters (Aparallactus) feed almost exclusively on centipedes, which they grab and chew. The prey quickly succumbs to the venom and is swallowed head first. The very elongate quill-snouted snakes feed almost exclusively on wormlizards (Monopeltis sp.). Larger species, such as the purple-glossed snakes (Amblyodipsas), eat small rodents as well as snakes, while the Natal black snakes (Macrelaps microlepidotus) also eat rain frogs (Breviceps sp.). The unusual fang erection of burrowing asps allows them to crawl past prey within the narrow confines of a burrow and envenomate the prey by stabbing backward.

Reproductive biology

All but one species are oviparous and lay small clutches (two to 15) of elongate eggs. These are laid in a dead termite nest or in moist soil beneath a rotting log or boulder, and take six to eight weeks to develop. Jackson's centipede eater (Aparallactus jacksonii) gives birth in June to two to three minute babies (about 4 in [10 cm]).

Conservation status

No species are threatened, although some have very restricted ranges.

Significance to humans

Although most aparallactines are harmless, the Natal black snakes require care. Its bite has caused nausea and loss of consciousness, although not death. All burrowing asps, however, are venomous and a few are dangerously so. The venom glands are large and in some species extend into the neck. The venom is unique among snakes and causes severe pain, swelling, local blistering, nausea, vomiting, and diarrhea. Bites from most species are mild, but deaths have been caused by three species. There is no effective antivenom. Most bites occur at night when the victim either treads on the snake or rolls over onto it while asleep. They are easily confused with harmless snakes.

Species accounts

List of Species

Variable quill-snouted snake
Southern burrowing asp

Variable quill-snouted snake

Xenocalamus bicolor

subfamily

Aparallactinae

taxonomy

Xenocalamus bicolor Günther, 1868, Zambezi (later corrected to Damaraland), Namibia.

other common names

English: Striped quill-snouted snake.

physical characteristics

The female is 28.5 in (72 cm) and the male 22.5 in (57 cm). This very thin, elongate snake has smooth scales in 17 midbody rows. The snout is extremely pointed with an underslung mouth. It is pale above with paired dark blotches or stripes; the belly is white.

distribution

From the southern parts of the Democratic Republic of the Congo, through Angola and western Zambia, to central South Africa and Mozambique.

habitat

Deep sandy soils with mixed savanna.

behavior

These bizarre burrowing snakes tunnel deep into sandy soils searching for their prey. They come to the surface only when searching for mates or after heavy rain. Gentle in the hand, they rarely bite but may give a sharp prick with their hard snout.

feeding ecology and diet

This snake is a specialist feeder on large wormlizards (e.g., Monopeltis sp.). How quill snouts manage to kill and overpower such large prey within the confines of their tight burrows remains a mystery—perhaps they stab them to death.

reproductive biology

Oviparous, they lay a few (up to four) elongate eggs in a chamber in moist sand. The young measure about 8 in (20 cm).

conservation status

Not threatened.

significance to humans

None known.

Southern burrowing asp

Atractaspis bibronii

subfamily

Atractaspidinae

taxonomy

Atractaspis bibronii A. Smith, 1849, eastern districts of the Cape Colony, South Africa.

other common names

English: Bibron's burrowing asp, side-stabbing snake.

physical characteristics

The female is 24.4 in (62 cm) and the male 26 in (66 cm). This short, stocky snake has smooth, close-fitting scales in 19–25 rows at midbody. It is uniformly purple-brown to black above. The belly is usually uniform dark gray, but sometimes white to cream with scattered dark blotches.

distribution

From the Northern Cape of South Africa, through Botswana, Namibia, and Angola to Tanzania and coastal Kenya.

habitat

Varied, ranging from savanna and semidesert to coastal thicket.

behavior

At night they may emerge on the surface, particularly after rain. Underground they use the side of the head to excavate a chamber beneath a sun-warmed stone. They have a peculiar "aromatic" smell, the function of which is unknown. On hard surfaces the neck is flexed, with the nose pointing down vertically, as they try to burrow.

feeding ecology and diet

The diet mainly includes other burrowing reptiles, but nestling rodents and small frogs are also eaten.

reproductive biology

Oviparous, they lay a few (usually four to seven, but up to 11) elongate eggs (1.1–1.4 in [27–36 mm] long by 0.4–0.5 in [10–12 mm] wide) in summer. The young measure about 6 in (15 cm).

conservation status

Not threatened.

significance to humans

These asps are responsible for many bites in rural areas. The glands yield minute amounts of straw-colored venom (1.3–7.4 mg), which causes immediate pain and local swelling. Mild neurotoxic symptoms (e.g., nausea, dry throat, and vertigo) may be present in the early stages, but necrosis is rare and no fatalities are known. Polyvalent antivenom unfortunately is ineffective.

Resources

Books

Branch, Bill. Field Guide to Snakes and Other Reptiles of Southern Africa. South Africa, 1998.

Spawls, Stephen, and Bill Branch. The Dangerous Snakes of Africa: Natural History, Species Directory, Venoms, and Snakebite. Sanibel Island, FL: Ralph Curtis Books, 1995.

Spawls, Stephen, et al. A Field Guide to the Reptiles of East Africa: Kenya, Tanzania, Uganda, Rwanda, and Burundi. San Diego: Academic Press, 2002.

Periodicals

Underwood, G., and E. Kochva. "On the Affinities of the Burrowing Asps Atractaspis (Serpentes: Atractaspididae)." Zoological Journal of the Linnean Society 107 (1993): 3–64.