Specimen Showcase | Big Star with Strange Feet
- Hong Kong Biodiversity Museum
- Apr 9
- 3 min read
The African clawed frog, 𝘟𝘦𝘯𝘰𝘱𝘶𝘴 𝘭𝘢𝘦𝘷𝘪𝘴 (Daudin, 1802) originates from Sub-Saharan Africa (Nigeria to Sudan to South Africa), but was later introduced to four other continents including North America, South America, Europe, and Asia. Despite its unusual appearance with its flattened body, two small eyes on top of head, and strange hind feet with black claws on the three interior toes, this amphibian has displayed extraordinary properties and become prominent in the field of biology.
Upon hatching from its egg, the young tadpole spends 99 % of its time hanging tail-down thanks to mucus secreted by a cement gland on its head; sticking itself to plants or other objects. While hanging, the tadpole remains motionless and is much less responsive to stimulation, giving predators some hard time finding it. Upon further development, it starts growing out limbs but also a very special structure that distinguishes this species from other ordinary tadpoles—a pair of whisker-like barbels near the mouth. The presence of these barbels is particularly beneficial for filter feeding, which helps the tadpole to efficiently locate food sources, such as tiny planktonic organisms, in its habitat.
In about 6 to 10 weeks, the tadpole would have successfully grown and metamorphosed into an adult-sized African clawed frog. Generally, male African clawed frogs measure 5 to 6 cm long while females are 10 to 12 cm long. Losing its signature barbels from its juvenile stage, the clawed frog adapts a brand-new diet thanks to several newly acquired features. It is now a scavenger that eats living, dead, or dying arthropods🦗 and other pieces of organic waste💩. It would even attack anything passing in front of it, just for a taste. What a glutton! To support such voracious appetite, the African clawed frog uses its extremely sensitive fingers🤚🏻, smell👃🏻, and even lateral line systems, which are usually found in fish to detect water vibration and locate food. It also has an awful eating manner. Being tongueless, African clawed frogs usually suck in the food and use forelimbs to push it into their mouth, with additional aid from the rapid forward thrust of their powerful hind limbs. If the food is too bulky, the frog uses its claws, a tool unique to the Pipidae family, to tear it apart. Such claws are also unusual if we compare them with those of other amniote animals. Generally, claws from animals, such as cats and mice, grow outward from the claw bed and become longer overtime. Yet, for the African clawed frogs, the tip of the claws is the first to develop, and then thickens inward overtime instead.
After 10 to 24 months, the African clawed frog reaches another stage of life, which is sexual maturity. Despite having no sound making organ, the clawed frogs would still produce sound through the contraction of their muscles present in the throat🗣️. The male would initiate the call of love, which sounds like alternating long and short trills. The female would then respond with either a pleased acceptance (a rapping sound) or a clear rejection (slow ticking sound). After that, the mating begins with the male grabbing the female's back and fertilizing the eggs as the female releases them. During this process, 500 to 1000 eggs would be laid. Egg laying, unlike in many other amphibian relatives, can take place during any season and up to four times a year. This unusual multiple egg laying behaviour caught the attention of scientists which then led to important discoveries.
Scientists showed that the egg laying behaviour within the African clawed frogs is dependent on certain hormone levels within females. On reaching a certain threshold of the specific tropic hormone, they would start laying eggs right away. Realising this property, researchers then developed a quick test for diagnosing early pregnancy through the injection of treated urine from pregnant women, which contains large amounts of the tropic hormone. Additionally, the eggs of the African clawed frog are also valuable for embryological studies🧬 and in other fields of research as experiment materials🔬, as they are large, produced in high quantities and easy to manipulate.
Curious about meeting this unusual frog and many other fascinating species in person? Come and visit the Hong Kong Biodiversity Museum to have a closer look and discover more about nature. If you enjoyed this post, feel free to share it with your friends and follow us for more posts.
Text: Felix Tan
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