Enormous frogs heave rocks to build tadpole ‘nests’

The world’s largest frog constructs ponds to protect its developing young — the first nest-building behaviour observed in any African amphibian.

The endangered Goliath frog (Conraua goliath) of western Africa measures 34 centimeters long, excluding its legs, and can weigh more than 3 kilograms. Mark-Oliver Rödel at the Leibniz Institute for Evolution and Biodiversity Science in Berlin and his colleagues heard tales from frog hunters that Goliath frogs heave rocks to create circular nests. To confirm these stories, the researchers surveyed a 400-metre-long section along the Mpoula River near Penja, Cameroon.

The water is calmer in a Goliath frog nest (background) than in the main river channel.Credit: Marvin Schäfe

They discovered 19 nests, averaging 1 metre in diameter, along the Mpoula’s banks. The nests ranged from simple clearings to gravel beds carefully encircled with rocks that weighed as much as 2 kilograms. The engineered structures shielded the nests’ interiors from rapidly flowing water and predatory fish, creating an oasis for eggs and tadpoles.

The researchers argue that the nests — which require their architects to move large, heavy items — could explain the evolution of these gigantic frogs.