he species is about 11 cm (4.3 in) long from snout to vent. The large head is broader than long, with a short rounded snout. Males are much larger than females. The former have a paired internal vocal sac and three short ridges of small black spines along the inner surface of the first manual digit. Breeding males also develop – somewhat hair-like – dermal papillae that extend along the flanks and thighs. These contain arteries and are thought to increase the surface area for the purpose of absorbing oxygen (comparably to external gills of the aquatic stage), which is useful as the male stays with his eggs for an extended period of time after they have been laid in the water by the female.
The species is terrestrial, but returns to the water for breeding, where egg masses are laid onto rocks in streams. The quite muscular tadpoles are carnivorous and feature several rows of horned teeth. Adults feed on slugs, myriapods, spiders, beetles and grasshoppers.
The hairy frog is also notable in possessing retractable « claws » (though unlike true claws, they are made of bone, not keratin), which it may project through the skin, apparently by intentionally breaking the bones of the toe. In addition, the researchers found a small bony nodule nestled in the tissue just beyond the frog’s fingertip. When sheathed, each claw is anchored to the nodule with tough strands of collagen, but, as Gerald Durrell discovered firsthand, when the frog is grabbed or attacked, the frog breaks the nodule connection and forces its sharpened bones through the skin.
This is probably a defensive behavior. Although a retraction mechanism is not known, it has been hypothesized that the claws later retract passively, while the damaged tissue is regenerated.
Amphibian researcher and biologist David Wake of the University of California, Berkeley, says that this type of weaponry appears to be unique in the animal kingdom, (although the Otton Frog possesses a similar « spike » in their thumb). Also David Cannatella, a herpetologist at the University of Texas, Austin, questions whether the bony protrusions are meant for fighting. They could allow a frog’s feet « to get a better grip on whatever rocky habitat they might be in, » he says.