Shovel-nosed frogs

(Hemisotidae)

Class Amphibia

Order Anura

Family Hemisotidae

Thumbnail description
Small frogs with powerful forelimbs and a hard, sharp snout for burrowing

Size
1–3 in (25–80 mm)

Number of genera, species
1 genus; 8 species

Habitat
Savanna

Conservation status
Not threatened

Distribution
Sub-Saharan Africa

Evolution and systematics

No fossils of this family are known. There is some evidence suggesting that this family is related closely to the rain frogs in the genus Breviceps, family Microhylidae. Another point of view is that these similarities follow from a common burrowing way of life and may not reflect a true relationship. No subfamilies are recognized.

Physical characteristics

These heavily built frogs have particularly robust skeletons associated with their burrowing habits. The species have a globular body, with short, muscular limbs. The well-muscled limbs end in short fingers and toes. The snout is sharp and has a hardened tip for digging, and a groove runs transversely behind the eyes. The frogs are smooth-skinned, with very small eyes. A large, flattened tubercle on the inner heel assists them in pushing headfirst into the soil. Adults are as small as 1 in (25 mm) and range in size to the largest, the spotted snout-burrower, at 3 in (80 mm). The back and sides are generally brown or purple with yellow spots or blotches.

Distribution

These frogs are found in the tropical savanna of sub-Saharan Africa, from Ethiopia, in western Africa, to South Africa and from sea level to 5,900 ft (1,800 m).

Habitat

Shovel-nosed frogs are native to open and wooded savanna where soils are sandy. The larvae are found in deep temporary pools with muddy substrates, and they occur together with tadpoles of many other species, such as Xenopus and Kassina.

Behavior

The frogs are active during the wet season, emerging from burrows after dark to feed. They are found in habitats that become very arid before the rains start. In the dry season they burrow deep into banks and the mud of hollows, where they estivate. Adults emerge after rain to feed on the surface, although they may tunnel like moles and catch underground prey, such as earthworms.

Feeding ecology and diet

Shovel-nosed frogs eat nocturnal termites. In captivity they readily eat earthworms. They can be found after rain, feeding on the surface. They hunt earthworms by digging tunnels just below the surface. The hardened, sharp snout enables these frogs to move rapidly through loose soil.

Reproductive biology

Breeding is initiated by the first rains of the season. The male calls from a concealed site under vegetation at the edge of pools, usually on wet mud. The calls are prolonged buzzes. The male clasps the female and is dragged into the burrow by the larger female, who digs. The male then fertilizes the eggs in the nest. Females mate with only one male. Females remain with the developing eggs, which are laid in a burrow or under a log or stone. About 150–200 eggs are laid in a compact mass, each egg 0.08–0.10 in (2–2.5 mm) in diameter within a capsule 0.12–0.16 in (3–4 mm) in size. Clutch sizes may be as small as 30–35. At the top of the clutch are numerous empty egg capsules, which help protect the clutch. The nest is situated a little back from the water. Continuing rains cause the ponds to fill, and the water rises to the level of the tadpoles and liberates them.

Conservation status

Most species are widespread, and all are common. In areas where lowlands are drained and converted to housing schemes, much of the frogs' habitat is lost. This is especially true of species that are found in prime tourist areas along the east coast of Mozambique and South Africa.

Significance to humans

None known.

Species accounts

List of Species

Marbled snout-burrower

Hemisus sudanensis

taxonomy

Hemisus sudanensis Steindachner, 1863, sub-Saharan Africa.

other common names

English: Marbled shovel-nosed frog, mottled shovel-nosed frog, pig-nosed frog, mottled burrowing frog.

physical characteristics

Large females reach 2.2 in (55 mm). The eyes are small, the forearms are massive, and the toes are slightly webbed. Coloration varies, with dark gray or brown marbling or spots on a paler brown background. A light vertebral line is often present.

distribution

Found in most of sub-Saharan Africa, excluding rainforests, from Senegal to Eritrea, western Ethiopia, and Somalia and south into southern Kenya and the northern and northeastern parts of South Africa.

habitat

Open savanna.

behavior

The frogs feed on the surface or hunt prey underground by digging tunnels.

feeding ecology and diet

These frogs eat a range of small insects and feast on winged termites when they emerge. They also readily eat earthworms.

reproductive biology

Females are attracted to calling males. The male clasps the female, and she digs headfirst into the soft mud near a temporary pool. The eggs are laid and fertilized in an underground burrow. The female may remain near the eggs, which develop into tadpoles in the nest. Rain causes the pool to fill, and the tadpoles swim out of the nest as it floods. In extreme cases the tadpoles swarm onto the back of the female, who carries them to water.

conservation status

Not threatened.

significance to humans

None known.

Spotted snout-burrower

Hemisus guttatus

taxonomy

Hemisus guttatus Rapp, 1842, northeastern South Africa.

other common names

English: Spotted shovel-nosed frog, spotted burrowing frog, eastern sharp-snouted frog.

physical characteristics

The female may reach 3 in (80 mm); this is the largest species of snout-burrower. The toes are not webbed, and the back pattern is quite distinct, with a number of yellow dots on a dark purple or brown background. The head is pointed and small, with very small eyes. The snout tip is hard and used for burrowing. The arms are muscular, and the fingers are thick and strong.

distribution

Recorded from the KwaZulu Natal lowlands between Hluhluwe and Durban through the interior of South Africa.

habitat

Areas of flat, sandy soil that flood during the rains.

behavior

Active after dark, when they feed and breed.

feeding ecology and diet

Eats burrowing prey, such as earthworms, also takes insects that are active on the surface at night.

reproductive biology

The advertisement call is a long, high-pitched buzz. Eggs are laid in chambers that are 5.9 in (15 cm) below the surface. Each clutch consists of some 200 eggs. Each egg is 0.10 in (2.5 mm) in diameter within a 0.16-in (4-mm) jelly capsule. The eggs are protected by a few top layers of empty jelly capsules.

conservation status

The species is not directly threatened, although parts of the coastal habitat are threatened by development.

significance to humans

None known.

Resources

Books

Channing, A. Amphibians of Central and Southern Africa. Ithaca, NY: Cornell University Press, 2001.

Periodicals

Kaminsky, S. K., K. E. Linsenmair, and T. U. Grafe. "Reproductive Timing, Nest Construction and Tadpole Guidance in the African Pig-nosed Frog, Hemisus marmoratus." Journal of Herpetology 33 (1999): 118–123.

Alan Channing, PhD