African Clawed Frog
Photo credit: © Brian Gratwicke, https://flic.kr/p/dFNYGb
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Species at a Glance
The African clawed frog is from a unique family of frogs called Pipidae that lack a tongue and visible ears. It was widely used as an experimental amphibian in laboratories and also became a popular pet species, leading to releases and escapes from captivity that have allowed this highly adaptable species to form invasive populations around the world.
This plump, medium-sized aquatic frog has a flattened body and a wedge-shaped head that is smaller than the body. Males are 5-6 cm (2.5 in) long and females are larger, reaching 10-12 cm (4 in). Instead of moveable eyelids, this species has a horny transparent covering that protects the small, upward turned eyes. The front limbs are small with unwebbed fingers and the hind legs are large and webbed. The three inside toes on the back feet have sharp black claws. The skin is smooth and slippery, except where the lateral line gives the appearance of “stitching”. It is multicolored on the back with blotches of olive-gray or brown and the underside is creamy white or yellowish. This frog has the ability to change its appearance to match its background; therefore, it can become dark, light, or mottled. A distinguishing characteristic is that males lack a vocal sac. Females also have a cloacal extension at the end of the abdomen.
No frog in North America resembles this species.
A water-dependent species, the African clawed frog occurs in a wide range of habitats, including heavily modified and degraded ecosystems. It prefers stagnant pools and quiet streams and tends to avoid large rivers and waterbodies with predatory fish. It can tolerate wide fluctuations in pH; however, metal ions are toxic to it. It leaves the water only when forced to migrate, crawling over long distances to other ponds. During dry conditions, this frog can burrow into the mud and lie dormant for up to a year.
The African clawed frog was introduced as a laboratory test species to be used in pregnancy tests after it was discovered that females would begin laying eggs when injected with a pregnant woman’s urine. It was in such high demand that large numbers were bred in captivity and a significant pet trade developed in the 1960s. It was intentionally released from laboratories around the world when new technologies for pregnancy diagnosis were developed in the late 1950s. Other modes of introduction include intentional releases of unwanted pets and escapes from aquariums, especially because of its long lifespan of up to 15 years.
Native to southern and western regions of Africa, the African clawed frog was shipped around the world in the 1940s and 1950s. In the Mid-Atlantic region, the frog is established in Virginia ponds, and has also been collected in North Carolina.
Note: Distribution data for this species may have changed since the publication of the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016), the source of information for this description.
The African clawed frog has a voracious appetite and will eat anything it catches, including native invertebrates, frogs, fish, and birds, as well as its own tadpoles. It can out-compete native frogs and other aquatic species and can act as a vector for parasites and diseases such as chytrid fungus that can be transmitted to native frogs. It can also secrete a skin toxin that may be harmful to predators, including native fish.
Information for this species profile comes from the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016).