Squeakers and cricket frogs

(Arthroleptidae)

Class Amphibia

Order Anura

Family Arthroleptidae

Thumbnail description
Mostly small, inconspicuous brown frogs

Size
The frogs are generally less than 1 in (25 mm) long, although some, like the East African species Arthroleptis tanneri, may exceed 2.4 in (60 mm)

Number of genera, species
8 genera; 77 species

Habitat
Forest

Conservation status
Not threatened

Distribution
Sub-Saharan Africa

Evolution and systematics

No fossils are known from this terrestrial family. There is an ongoing debate concerning the relationships of this group. The consensus appears to be that it is not a subsection of the Ranidae, and should retain its status as a discrete family. Two subfamilies are recognized—the Arthroleptinae and the Astylosterninae—although an alternative classification regards each as a distinct family. The characteristics of the Arthroleptinae include a typical hourglass pattern on the back, and the presence of an elongated third finger in males. The characteristics of the Astylosterninae include bent fingers with projecting bony tips.

Physical characteristics

These are smooth-skinned terrestrial frogs. A longitudinal middorsal fine skin ridge is characteristic of the Arthroleptinae. Webbing is absent between the toes. Some species have enlarged disks on the fingers and toes. The frogs are mostly less than 1 in (25 mm) long, although some, like the East African species A. tanneri, may exceed 2.4 in (60 mm). The limbs and body are gracile in most species, although some of the burrowing species are robust and have robust limbs and flattened tubercles on the heel. A characteristic arthroleptine pattern is a dark hourglass or series of diamond-shaped markings along the dorsal midline. The background color varies greatly within a species, and can range from red to olive. Adult males in the Arthroleptinae have extremely long third fingers. In some species the finger may reach 40% of the body length. The astylosternines are mostly large frogs associated with fast-flowing streams in forests. The subfamily is distinguished on small differences in anatomy; most have curved sharp terminal phalanges that protrude through the skin of the finger tip.

Distribution

The family is found throughout tropical Africa from sea level to 9,800 ft (3,000 m) in forest or wooded savanna. The ranges are decreasing as the African rainforest is being destroyed.

Habitat

The frogs are known from the moist tropics, where they are found in leaf litter. The arthroleptines are inhabitants of

natural forests, but will live in any dense vegetation. Many astylosternines are associated with rapidly flowing torrents on forested slopes. There are no free-swimming larvae in Arthroleptinae, whereas large, well-muscled astylosternine larvae develop in fast-flowing streams.

Behavior

The adults are active throughout the year, with peaks of feeding and breeding after rain. They emerge only after dark in more open habitats, but can be found active in the shaded forest during the day. In areas where there is a distinct dry season they estivate. Males engage in combat with other males during the breeding season, in an effort to hold a breeding territory.

Feeding ecology and diet

The leaf litter frogs eat minute insects and other arthropods like small spiders, as well as other frogs. The larger, more robust species will eat anything that moves, providing it can be forced into the mouth. The terrestrial frogs move through the leaf litter taking small moving arthropods. The river dwellers feed along the edge of the water.

Reproductive biology

Arthroleptines are terrestrial breeders with direct development. Large, yolky eggs are laid in a hollow nest on the ground and develop into small adults without a free-swimming tadpole stage. Astylosternines deposit eggs in quiet backwaters of streams; they develop into torrent-adapted tadpoles. There are peaks of calling after rain, and most egg clutches are laid during the start to middle of the rainy season. In moist forests near rivers, breeding takes place over an extended period. Male arthroleptines call from concealed sites in leaf litter, although some species like the common squeaker sometimes call in the open from ground level. Astylosternine males call from the shallow edges of rivers. The eggs of arthroleptines are laid in small clutches under dead leaves. In these moist surroundings they hatch rapidly into juveniles, passing through a tadpole stage in the egg. There is no direct parental care, although the males of some species attract more than one female into the breeding territory, effectively placing the eggs from previous females within his care. Little is known of astylosternine breeding, but the hairy frog, Trichobatrachus robustus, remains underwater near the eggs, apparently to protect them from predators.

Conservation status

This is an endemic African family. Squeakers are common, and it is not unusual to see two or three along every step of a forest path or along the bank of a river. As the African forests are being logged, the available habitat is contracting, and the populations of all the forest amphibians are becoming smaller.

Significance to humans

The small arthroleptines are not of direct importance to humans; they are not eaten and they are not toxic. The larger astylosternines, such as the hairy frog, are a prized food of local people.

Species accounts

List of Species

Common squeaker

Arthroleptis stenodactylus

subfamily

Arthroleptinae

taxonomy

Arthroleptis stenodactylus Pfeffer, 1893, central and southern Africa.

other common names

English: Shovel-footed squeaker, dune squeaker, savanna squeaking frog, Kihengo screeching frog.

physical characteristics

This is a robust species, with relatively short legs. The inner metatarsal tubercle is large, spadelike, and as long as, or longer than, the first toe. The pattern on the back consists of a pair of dark sacral spots, with various combinations of a three-lobed dorsal band. In some animals a pale vertebral line is present. A dark line runs from the tip of the snout to the shoulder.

distribution

This species is widespread, known from southern and eastern Democratic Republic of the Congo to Kenya and southward to northern South Africa, Zimbabwe, and Mozambique.

habitat

It is often associated with leaf litter. It can be found at altitudes from 130 to 6,600 ft (40–2,000 m). This frog is very common, and is able to live in gardens and natural vegetation.

behavior

This species is active during the day in the wet season. The frogs move around searching for food.

feeding ecology and diet

This frog appears to eat a wide range of insect and other arthropod prey, as well as earthworms, snails, and even other frogs.

reproductive biology

The male calls from concealed sites in leaf litter and under vegetation, during the day and night after rain. Eggs are deposited in hollows or burrows in damp earth, often under bushes or around the roots of trees, or under loose leaf mold. Eggs are 0.1 in (2.5 mm) in diameter, creamy white, and deposited in clutches of 33–80.

conservation status

This species is widespread and common, able to live around human habitation, and not specifically threatened.

significance to humans

The common squeaker may live around human habitation, but has no direct significance as food or in any other way.

Tanner's litter frog

Arthroleptis tanneri

subfamily

Arthroleptinae

taxonomy

Arthroleptis tanneri Grandison, 1893, west Usambara Mountains, Tanzania.

other common names

English: Tanner's squeaker.

physical characteristics

This is the largest arthroleptid—females exceed 2.4 in (60 mm). They are robust, with no expanded disks on the fingers or toes, nor webbing between the toes. The skin of the back is smooth. The back is brown with indistinct darker chevron-shaped markings. A dark band runs from the nostril through the eye to the upper arm. The limbs are crossbanded.

distribution

This species is confined to highland forest in the west Usambara Mountains of Tanzania.

habitat

This species prefers forest floor habitats and may be found along streams in the forest.

behavior

The frogs sit and wait along streams or in leaf litter for insect prey during the day.

feeding ecology and diet

Tanner's litter frog eats forest-floor arthropods, including small spiders.

reproductive biology

Males call from the ground, well camouflaged in the leaf litter. The eggs are laid in clutches of about 30 eggs in hollow nests under the cover of dead leaves. The young emerge directly without a free-swimming tadpole stage.

conservation status

Not listed by the IUCN, though this species is restricted to a small forest patch at Mazumbai, as the rest of the west Usambara Mountains have been cleared of natural forest.

significance to humans

None known.

Bush squeaker

Arthroleptis wahlbergii

subfamily

Arthroleptinae

taxonomy

Arthroleptis wahlbergii Smith, 1849, eastern South Africa.

other common names

English: Wahlberg's screeching frog.

physical characteristics

Females are larger than males and attain lengths of 1 in (25 mm). The inner metatarsal tubercle is small, rounded, and less than half the size of the inner toe. The tips of the fingers and toes do not possess disks, although they may be swollen. The color pattern of the back is variable. Tan and darker brown background colors are typical. An hourglass pattern is common, and a pale vertebral stripe is found in some specimens.

distribution

This species is endemic to the tropical east coast of South Africa, and in suitable adjacent habitats inland.

habitat

It is found under leaf litter at the base of dense bushes. This species occurs in forest or thick bush, and is common under lush hedges and shrubs in gardens.

behavior

This small frog is very secretive, rarely coming into the open, and then only after the start of the rains. Diligent searching for days for the same calling male is often fruitless.

feeding ecology and diet

This frog is known to eat a wide range of insect prey, such as crickets, cockroaches, beetles, and grasshoppers, as well as other arthropod prey like spiders and centipedes. They also eat earthworms, snails, and even other frogs.

reproductive biology

The call is a long, high-pitched "wheep" or "wheepee." The eggs are pale and about 0.1 in (2.5 mm) within a capsule of 0.2 in (5 mm). Clutches of 11–80 eggs are known. Eggs are laid 0.8–1.2 in (20–30 mm) below the surface of the leaf litter, usually beneath bushes or other dense vegetation. The tadpole stage is passed in the egg. Eggs have been found in shallow burrows with an adult in attendance.

conservation status

Not threatened.

significance to humans

This species is able to successfully coexist with humans even in large cities like Durban.

Ugandan squeaker

Schoutedenella poecilonotus

subfamily

Arthroleptinae

taxonomy

Schoutedenella poecilonotus Peters, 1863, West Africa.

other common names

English: West African screeching frog.

physical characteristics

This is a small frog with a blunt snout. The head is broad and the body is squat. Females can be as large as 1.1 in (28 mm). The skin is quite smooth with small warts, although some individuals have a granular skin. There is no webbing between the toes. The color of the back varies from reddish to light tan with a dark pattern.

distribution

The Ugandan squeaker is found throughout the forest belt from West Africa to Uganda. There is some confusion with other species.

habitat

This frog is found in the forest, and also in peripheral savanna where there is lush vegetation.

behavior

The frogs move slowly along the ground taking small prey that move nearby.

feeding ecology and diet

This squeaker feeds on small leaf-litter arthropods.

reproductive biology

Males call from beneath dead leaves on the ground. Females lay clutches of 10–25 large, yolky eggs of 0.1 in (3 mm) in diameter. Each female may lay two or more clutches. The frogs only survive one breeding season, and have a recorded longevity of around six months.

conservation status

This species is not threatened, although the general concerns of the loss of forest habitat apply.

significance to humans

None known.

Crowned forest frog

Astylosternus diadematus

subfamily

Astylosterninae

taxonomy

Astylosternus diadematus Werner, 1898, Cameroon.

other common names

None known.

physical characteristics

The female is much smaller than the male. The largest frogs are 2.7 in (70 mm) in length. There is a distinct marking on

the head, and the underside is characteristically white or yellow with many dark spots.

distribution

This species is known from southwestern Cameroon and extreme eastern Nigeria at high elevations.

habitat

This frog is known from high savanna and dense mountain forest.

behavior

The frogs are active during the day, with peaks of feeding activity after dark.

feeding ecology and diet

These frogs eat a range of small arthropods found on the forest floor.

reproductive biology

Eggs are laid in quiet backwaters of streams. The tadpoles move into faster water as they grow. Although the tadpoles are found in fast-flowing streams, they do not have large sucker mouths.

conservation status

Not threatened.

significance to humans

None known.

Hairy frog

Trichobatrachus robustus

subfamily

Astylosterninae

taxonomy

Trichobatrachus robustus Boulenger, 1900, West Africa.

other common names

French: Grenouille poilve; German: Haarfrosch.

physical characteristics

The frog is stocky, up to 5.2 in (130 mm) in males, although the females only attain 3.6 in (90 mm), with darker markings on a brown background. The throat is yellow. During the breeding season, the sides of the thighs and body of the male develop small hairlike outgrowths. These increase the surface area for the uptake of oxygen. This fringe gives the frog its common name. The tadpole has an oral disk and a large suckerlike disk on the abdomen.

distribution

This frog is known from eastern Nigeria to Equatorial Guinea.

habitat

Hairy frogs are found in dense forest along streams.

behavior

The frogs are terrestrial during most of the year, and feed along the forest floor. When the rains set in and the breeding season starts, the females remain in the forest to feed while the males move into the streams. Once the females are ready to breed they join the males in the water.

feeding ecology and diet

This species feeds along the edges of streams and on the forest floor. They eat a range of insects and other arthropods.

reproductive biology

Eggs are laid in fast-flowing rivers. The male attends the egg clutches underwater, presumably to protect them from predators. The fringe of hairlike papillae enables him to remain underwater for days without needing to come to the surface for air.

conservation status

Not threatened. This species is widely distributed and not in need of any conservation action.

significance to humans

Large hairy frogs are collected and eaten by local people, although not in significant numbers.

Resources

Books

Channing, Alan. Amphibians of Central and Southern Africa. Ithaca, NY: Comstock Publishing Associates, 2001.

Passmore, Neville, and Vincent Carruthers. South African Frogs: A Complete Guide. Revised edition. Halfway House, South Africa: Southern Book Publishers and Johannesburg: Witwatersrand University Press, 1995.

Rödel, Mark-Oliver. Herpetofauna of West Africa. Vol. 1, Amphibians of the West African Savanna. Frankfurt: Chimaira, 2000.

Alan Channing, PhD