An African clawed frog's body is flattened with a smaller, wedge-shaped head. The positioning of the eyes and nostrils on the top of the head, along with camouflaged skin, help this species hide from predators, such as herons. The smooth skin is often multicolored with blotches of greenish-gray or brown on its back. The underside is off-white with a yellow hue. African clawed frogs have the ability to change their appearance to match their background, becoming darker, lighter or mottled.
The frogs' front limbs are small with non-webbed fingers used to push food into the mouth. Their hind legs are large and webbed, and the three inside toes on either foot have "claws," which are not true claws but cornified tips. Although an adept swimmer, the African clawed frog is clumsy on land and crawls rather than hops.
African clawed frogs also have a lateral line system that is very sensitive to vibrations, enabling them to detect predators and prey in murky water. The lateral line is visible as a series of white stitch marks along each side of the frog.
The Pipidae family of frogs is unique in that members lack a tongue and a visible ear. The males also lack vocal cords. Instead of moveable eyelids, a horny, transparent covering protects their eyes.
Males weigh 2 ounces (60 grams), and are about 2 to 2.5 inches (5 to 6 centimeters) long. Females are much larger, weighing approximately 7 ounces (200 grams) and are about 4 to 4.5 inches (10 to 12 centimeters) long. Females also have cloacal extensions at the end of their abdomen.
These frogs live along the African Rift Valley south of the Sahara Desert in east and southern Africa, as well as in South Africa, Namibia and Angola. As an invasive species, they are now found in freshwater areas all over the world, including the United States, Chile, France, Indonesia, Portugal, United Kingdom and Italy. Rarely found in running streams, the African clawed frog prefers warm, stagnant pools and quiet streams, thriving in temperatures from 60 to 80 degrees Fahrenheit. Almost totally aquatic, it only leaves the water when forced to migrate to another pond. It is a highly opportunistic species and can easily colonize newly created water bodies.
Despite their lack of vocal cords, males can vocalize to attract females. Rapid muscle contractions in the throat produce a clicking noise, to which the female responds with either an acceptance call (a rapping sound) or a rejection call (slow ticking sound). A female only rarely answers the male's call.
As tadpoles, African clawed frogs are exclusively filter feeders. Adult frogs become scavengers, eating living, dead or dying arthropods and other pieces of organic waste, including aquatic insect larvae, water insects, crustaceans, small fish, tadpoles, worms and freshwater snails. They have a voracious appetite and will attack anything that passes by. Extremely sensitive fingers, an acute sense of smell and its lateral line system help to locate food. A special pump helps individuals suck food into their mouths. The claws on their hind feet tear apart larger pieces of food.
These frogs are sexually mature in 10 to 12 months. Mating can take place during any time of year but is most common from early spring to late summer, depending on location, and can take place up to four times a year. Despite their lack of vocal cords, males vocalize to attract females.
Mating usually occurs at night in stagnant water, and lasts three to four hours. The males clasps a female around the pelvic region, a form of amplexus (a common mating position in which the male grabs the female from behind), in opposition to the normal axillary, or front limb, amplexus. As amplexus is formed, the female lays 500 to 2,000 eggs. Sticky jelly around the eggs causes them to adhere to objects such as sticks, stones and other substrate underwater. Eggs hatch within one week and tadpoles are slightly less than 1/5 of an inch (2/5 of a centimeter) long. The total change from egg to small frog takes about six to eight weeks. Adults exhibit no parental care.
African clawed frogs can live up to 15 years.
African clawed frogs are a very successful and adaptable species with a wide distribution and presumed large population.
These frogs have been used extensively as laboratory research animals, mostly in the field of vertebrate embryology because females are prolific egg layers and the embryos are transparent, making it easy to observe its development.
During the 1940s, female African clawed frogs were used as indicators of human pregnancy. Female frogs were injected with urine of a human female, and the injected frog would start producing eggs if the woman was pregnant. With the adoption of modern-day pregnancy tests, many African clawed frogs were released all over the world, creating an invasive species problem in some areas and possibly spreading the chytrid fungus. Seemingly, the disease does not detrimentally affect populations of African clawed frogs.
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