Tree frogs hang their eggs from branches

In southern Africa, the grey tree frog has evolved an original means of protecting its eggs from predators and keeping them moist at the same time. The frog spends most of its life in trees, and at egg-laying time, in the rainy season, the female carries her smaller mate to a tree branch overhanging a short-lived pond or puddle. Here the pair may be joined by several more males, and together they begin to build a nest from a liquid excreted by the females.

In the cool of night, the males beat the liquid into a foam with their hind legs, rather in the way that cooks beat egg whites. The female then lays her eggs, which are fertilised by her mate as they emerge, into this foamy nest.

The morning sun turns the nest into a half-baked meringue, with a hard-crusted outer surface round a moist interior. The eggs develop inside, safe from the drying sun and birds, until the tadpoles are ready to emerge and slip into the water below.