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

Resources

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

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.

[Article by: Alan Channing, PhD]