Amphibians
Hip-pocket Frog
Assa darlingtoni · also called hip-pocket frog, pouched frog, marsupial frog
The hip-pocket frog is one of the smallest frogs in Australia and one of the strangest parents anywhere. When its eggs hatch, the tadpoles do not head for water — they climb up the father’s body and slide into a pair of skin pockets on his hips, where they stay, sealed inside him, until they crawl back out weeks later as tiny finished froglets.
Overview
The hip-pocket frog lives only in the cool upland rainforest of the Queensland and New South Wales border ranges, in wet leaf litter and moss above about 500 m. It is only 1.6–2.4 cm long, brown, and well camouflaged. It eats mites, springtails, and other tiny litter invertebrates.
Pockets on the hips
The male has two pouches, one opening on each flank near the hind leg, formed by folds of skin and inconspicuous when empty. The eggs are laid on land and guarded by the male; when they hatch, the tadpoles wriggle up his body and into the pockets.
No water needed
Inside the pouches the tadpoles live off their yolk for seven to nine weeks and never enter open water, emerging as fully formed froglets. This lets the species breed in damp forest litter with no pond nearby — useful in its cool, wet mountaintop home.
A lone survivor of its kind
It belongs to the Australian frog family that also held the two gastric-brooding frogs, which raised young in the stomach and are now extinct. The hip-pocket frog is the only living frog that broods its young in pouches like this.
Status
The hip-pocket frog is Vulnerable and declining. Its small, high-elevation rainforest is warming and drying, fire is reaching it more often, and it is exposed to the amphibian fungal disease chytridiomycosis.
Hip-pocket Frog: common questions
How does the hip-pocket frog carry its young?
The male has two small pouches, one on each side of the body near the base of the hind legs, formed by folds of skin that are barely visible when empty. The female lays a small clutch of eggs on damp ground in the leaf litter, and the male stays with them. The eggs develop into tadpoles inside the jelly, and at hatching the tiny tadpoles squirm out and wriggle up over the male's back and sides until they find the pouch openings and slide in, several to each pocket. He then carries them, hidden inside his own body wall, for the rest of their development.
Do the tadpoles ever go in water?
No, and that is the point of the system. Once inside the male's hip pockets the tadpoles are sealed away from the outside world and live entirely on the yolk they hatched with, taking around seven to nine weeks to complete metamorphosis. When they are ready they crawl back out of the pouches as fully formed froglets only a few millimetres long. Because the whole aquatic phase happens inside the parent, the hip-pocket frog can breed in wet forest litter with no pond or stream nearby, which suits its cool, damp mountaintop habitat.
Is it the same as the gastric-brooding frog?
They are relatives but not the same. Both belong to an Australian family of ground frogs, and both evolved a way of protecting their young inside the parent's body. The two gastric-brooding frogs, now extinct, swallowed their eggs and raised the tadpoles in the mother's stomach, then brought up finished froglets. The hip-pocket frog uses external skin pouches on the father instead. With the gastric-brooding frogs gone, the hip-pocket frog is the only living frog that broods its young in pouches like this.
Why is the hip-pocket frog threatened?
It lives only in a small pocket of cool, wet, high-elevation rainforest along the Queensland and New South Wales border, and that habitat is shrinking and warming. Climate change is drying and heating its mountaintop refuges, and it has nowhere higher to go. Fire, which historically rarely reached these wet forests, is becoming more frequent and severe and can kill frogs directly and destroy the moist litter layer they depend on. The frog is also exposed to chytridiomycosis, the fungal disease affecting amphibians worldwide. Together these have pushed it onto the threatened list.