Amphibians
Amazon Milk Frog
Trachycephalus resinifictrix · also called Amazon milk frog, mission golden-eyed tree frog, blue milk frog
The Amazon milk frog is a big, handsome, marbled tree frog that spends its whole life high in the rainforest canopy and almost never touches the ground. Grab one and it oozes a sticky white poison — the “milk” of its name — and its young, raised in a puddle inside a tree, grow up eating each other.
Overview
Amazon milk frogs live in lowland rainforest across the Amazon basin, entirely in the canopy. They are nocturnal insect hunters, pale bluish-grey to tan with brown banding and gold eyes crossed by a cross-shaped pupil. They are rarely seen because they do not come down — they even breed high in the trees.
The “milk”
Handled or stressed, the frog’s skin glands exude a thick, sticky, opaque white fluid (the species name means “resin maker”). It is a defensive toxin — bitter, irritating, and clinging to a predator’s mouth — and the source of the common name. It stings human eyes, so the frog should be handled minimally.
Breeding in a tree
The Amazon milk frog is a tree-hole breeder. A male calls from inside a water-filled cavity in a trunk, his voice amplified by the chamber, and a female lays eggs as a film on the water within it. Everything happens in that isolated pocket, sometimes metres up.
Cannibal tadpoles
A tree hole holds almost no food, so the tadpoles are aggressive and carnivorous — eating the unfertilised “nurse” eggs the female returns to provide, and each other. This thins the brood to a number the water can support.
Status
The Amazon milk frog is Least Concern, widespread in Amazonian forest and locally common. It is a popular, widely captive-bred pet, so wild collection is not a major pressure.
Amazon Milk Frog: common questions
Why is it called a "milk" frog?
Not because of any connection to milk as a food, but because of what the frog does when it is handled roughly or feels threatened — glands in its skin release a thick, sticky, opaque white fluid that looks like milk or latex (the species name resinifictrix means "resin maker"). This secretion is a chemical defence. It is bitter and irritating, sticks to a predator's mouth and gums, and deters birds, snakes, and mammals from eating the frog. It is not dangerously toxic to humans, but it can sting the eyes and mucous membranes, so the frog should be handled as little as possible and hands washed afterwards, as with any amphibian.
What does it mean that it's a "tree-hole breeder"?
Instead of laying its eggs in a pond or stream, the Amazon milk frog breeds in phytotelmata — small bodies of water that collect inside natural cavities, especially the water-filled hollows in the trunks and branches of large rainforest trees. A male calls from inside such a cavity, his voice boomed out by the acoustic chamber, and a female that comes to him lays eggs as a film on the water surface. The eggs hatch and the tadpoles develop entirely within that isolated pocket of water, sometimes many metres above the ground. This lifestyle frees the frog from ground-level and pond predators and competitors, but confines development to a tiny, nutrient-poor space.
Why do the tadpoles eat each other?
Because a tree hole contains very little food. The water that collects inside a tree cavity has few of the algae, detritus, and micro-organisms that fuel a normal pond tadpole, so milk frog tadpoles are forced to be opportunistic and often carnivorous. The main food source the female provides is unfertilised "nurse" eggs, which she returns to lay into the cavity for the tadpoles to eat, but the tadpoles are also aggressive toward each other, and larger, faster-growing individuals will cannibalise smaller siblings. This thins the brood down to a number the tiny water body can support, and the survivors metamorphose and disperse into the canopy.
Is the Amazon milk frog a good pet?
It is one of the most popular large tree frogs in the amphibian hobby and is widely captive-bred. It is considered a good choice for a keeper with some experience — it is hardy, striking, long-lived, active and vocal, and does well in a tall, planted, humid terrarium at warm room temperature with a water feature, a UVB light, and a diet of appropriately sized insects. The usual amphibian rules apply — clean dechlorinated water, minimal handling because the skin absorbs contaminants, and space, since these frogs grow large. Wild collection is not a significant pressure on the species because captive breeding meets demand.