Lesser Bornean Narrow-mouthed Frog

Microhyla borneensis is a very small species with a snout–vent length of about 18 mm (0.71 in) for females and around two thirds of this for males. It has a broadly triangular body that is flattened dorso-ventrally. The snout is obtusely pointed, the eyes are small and have round pupils and there are no visible tympani. The skin on the dorsal surface may be smooth or bear tubercles and that of the ventral surface is always smooth. The limbs are short. The hands are unwebbed and the outer digits are spatulate. The digits of the feet are partially webbed. M. borneensis has less webbing on its feet than most frogs, which may be beneficial when trying to climb the sides of the pitcher plants, which can be slippery. The dorsal surface of this frog is reddish-brown, the throat is mottled brown and the ventral surface is pale.

Microhyla borneensis is known from the Matang Range in Sarawak, Borneo, but it is presumably widespread in suitable habitats in the lowlands of northern Borneo. M. borneensis is found near Mount Serapi in Kubah National Park, Sarawak, Borneo. It spends much of its life cycle in the traps of the pitcher plant Nepenthes ampullaria, after which it is named. It is therefore considered a nepenthebiont. This is not particularly unusual; in fact, it shares this environment with a species of crab spider, Henriksenia labuanica, which is also commonly found in Nepenthes pitchers. This spider's former binomen, Misumenops nepenthicola, and that of the related species of Singapore, Henriksenia nepenthicola, had the specific epithet nepenthicola applied for this reason.

Microhyla borneensis breeds in the water-filled pitchers of Nepenthes ampullaria, a pitcher plant that is a feature of the floor of the Borneo rainforest. Multiple clutches may be laid in the same pitcher which may contain tadpoles of different ages. Metamorphosis takes place about a fortnight after the eggs are laid.