Amphibians
Waxy Monkey Tree Frog
Phyllomedusa sauvagii · also called waxy monkey frog, painted-belly leaf frog
The waxy monkey tree frog is a frog that behaves like a lizard. It lives in dry thorn forest where the air should suck it dry, it basks in full sun, and it survives by literally waterproofing itself — wiping a home-made wax over every part of its body with slow, deliberate sweeps of its own legs.
Overview
Waxy monkey tree frogs live in the Gran Chaco, the hot, semi-arid belt of thorn forest and savanna covering northern Argentina, Paraguay, Bolivia, and southwestern Brazil. They are nocturnal hunters of insects and spend the day perched, often exposed, in shrubs and trees. They are pale sage green above with a white belly and orange-and-white spotting along the flanks and inner legs.
The wax coat
Ordinary frog skin loses water fast, which is why most frogs stay in the shade and the damp. This species instead produces a lipid secretion from skin glands and applies it in a fixed wiping sequence — each leg drawn methodically across the body — until it is covered in a thin waterproof film. This cuts evaporative loss to roughly a tenth of a normal frog’s, close to what a reptile experiences.
Living like a reptile
Sealed in wax, the frog does things frogs are not supposed to do. It basks in direct sun, letting its body temperature rise past 30 °C. And it excretes uric acid as a paste rather than flushing nitrogen waste out in watery urine, the same water-conserving trick used by birds and lizards. These adaptations let it occupy habitat that would otherwise be closed to amphibians.
Movement and breeding
The “monkey” name comes from its walking gait — it moves hand-over-hand along branches, grasping each twig with an opposable toe, rather than hopping. To breed, a pair descends to a pond, and the female, clasped by the male, folds a leaf over the clutch above the water; when the eggs hatch, the tadpoles drop into the pond below.
Status
The waxy monkey tree frog is Least Concern, common across the Chaco and heavily captive-bred for the exotic-pet trade. Its skin peptides are of interest to drug researchers for antimicrobial and analgesic activity.
Waxy Monkey Tree Frog: common questions
Why does the waxy monkey frog cover itself in wax?
To stop drying out. Frog skin is normally very leaky to water, which confines most frogs to damp, shaded places. The waxy monkey frog lives in the Gran Chaco, a hot, seasonally arid region, and it solves the water problem behaviourally. Glands in its skin produce a mixture of lipids, and after emerging the frog performs a stereotyped "wiping" routine, drawing each leg across its body in sequence until it is sealed in a thin waxy film. This reduces evaporative water loss to roughly a tenth of a normal frog's — comparable to a lizard — and lets the frog stay out in the open, and even in the sun, without desiccating.
Is it true this frog basks in the sun?
Yes, which is very unusual for an amphibian. Once waterproofed, the waxy monkey frog will sit fully exposed on a branch through the day, letting its body temperature climb above 30°C. It backs this up with another reptile-like trait — instead of excreting nitrogen waste as dilute urea in lots of water, like most frogs, it excretes it as a thick paste of uric acid, the same water-saving strategy birds and lizards use. Together these adaptations let a frog live where the climate should exclude frogs entirely.
Why is it called a "monkey" frog?
For the way it moves. Rather than the explosive hop of a typical frog, Phyllomedusa species walk slowly and deliberately along branches, reaching out and grasping the next twig with feet that have an opposable first toe, much like a small primate climbing. Combined with their large forward-set eyes and unhurried manner, this gives them a distinctly monkey-like appearance in motion. The "waxy" part of the name is the skin coating, and "leaf frog" refers to their leaf-green colour and leaf-fold nests.
Are waxy monkey frogs poisonous?
Their skin secretions contain a range of bioactive peptides, some with antimicrobial and painkilling properties that have attracted pharmaceutical research, and the secretions can be irritating. This is not the same as the lethal toxicity of a poison dart frog; the compounds are defensive irritants and the frog is not dangerous to handle carefully, though as with any amphibian you should not touch your eyes or mouth afterwards and should wash your hands. In parts of South America a related species' secretion, "kambô," is used in traditional cleansing rituals, a practice that carries real medical risks.