Amazon Milk Frog

The Amazon milk frog, also called the Mission golden-eyed tree frog, is a large arboreal frog native to the Amazon rainforest in South America. It was first discovered along the Maracanã River in Brazil. Adults reach 6.4 to 10.2 cm in length and are light grey with brown or black banding, while juveniles show stronger contrasts. Populations are widespread in Guyana, Colombia, Brazil, Ecuador and Peru, where the frogs often live in vegetation extending over permanent, slow-moving water. The common name refers to the milky fluid the frog produces when stressed or threatened. Its blood tends to be a shade of blue that shows through the skin, most boldly around the mouth and toe pads.

About the Amazon milk frog

The Amazon milk frog, also called the Mission golden-eyed tree frog, is a large tree frog of the family Hylidae that lives high in the canopy of the Amazon rainforest in South America. It gets its name from the sticky, milk-white fluid its skin releases when the frog feels threatened.

Scientists call it Trachycephalus resinifictrix. It was first described in 1907 by Goeldi, who named it Hyla resinifictrix and noted its unusual breeding habits. It was first found along the Maracanã River in Brazil. The species was later placed in the genus Phrynohyas, which has since been merged into Trachycephalus.

For a tree frog it is big. Adults reach about 6.4 to 10.2 cm (2.5 to 4 in) long. Males reach around 8 cm (3.1 in) and females about 10 cm (3.9 in).

Adults are light grey or dark brown with broad dark or pale bands, blotches and spots. Descriptions differ in which tone they call the base color, but all describe a strongly banded frog. Young frogs have the same basic pattern with sharper contrast. As the frog ages, its skin becomes slightly bumpy.

The belly is cream, shading to bluish toward the flanks. One of the species' oddest traits is its color inside: the blood has a bluish tint that shows through the skin, most clearly in the mouth and on the toe pads. The bones and muscles have been described as bluish too.

The iris is marked with a cross shape that is characteristic of the species. The large toe pads let it grip leaves and branches.

Behavior and diet

The Amazon milk frog is nocturnal and almost entirely arboreal. It lives in the canopy of rainforest growing on dry, unflooded ground, and it can be very hard to spot from the forest floor. It spends its life in the trees, and it lays its eggs there too.

Its main defense is the "milk" in its name. Glands on its back release a sticky, white, milky secretion when the frog is stressed or attacked. This fluid is not considered dangerous to people. Its job is to make the frog taste bad and to irritate the mouth of a predator that tries to eat it.

Adults are carnivores. They eat insects and almost any other small animal they can overpower. Tadpoles feed mostly on algae, detritus and eggs.

Males have very large vocal sacs and are extremely loud. Their call is powerful enough to carry several hundred meters through the forest. Males are occasionally heard calling from ponds or wheel ruts on the ground, though it is not known whether breeding there succeeds.

Breeding is not tied to a fixed season, but it happens during the rains. The frogs breed in large water-filled cavities in the crowns of big trees, some of them as high as 30 m (about 100 ft) above the ground. These little pools are known as phytotelmata.

Over several bouts, a female can lay up to 3,000 eggs into the water in the hollow. The tadpoles hatch after about a day. In their early stage they still have external gills.

What happens next is unusual. The tadpoles feed on unfertilized eggs in the clutch. After a male has mated, he keeps calling to attract another female, and her eggs become food for the tadpoles already in the pool. Scientists call tadpoles that eat eggs this way oophagous.

Metamorphosis into a young frog takes about three weeks.

Range and habitat

The Amazon milk frog is found across the Amazon region of South America. Recorded countries include Brazil, Bolivia, Peru, Ecuador, Colombia, Venezuela, Guyana, Suriname and French Guiana. It lives at elevations up to about 450 m (1,480 ft). In Venezuela its presence is reported by some sources but treated as likely rather than certain by others.

Its home is tropical rainforest. It keeps to the canopy and often lives in vegetation hanging over permanent, slow-moving water. Wild frogs experience temperatures of about 21 to 30 °C (70 to 86 °F).

That canopy lifestyle makes the species hard to study. Because it lives, calls and breeds high in the trees, sometimes 30 m (about 100 ft) up, and is active mainly at night, it is often very difficult to observe from the ground.

Conservation status

The Amazon milk frog is listed as Least Concern on the IUCN Red List, in its most recent assessment, published in 2023. It is widespread across a huge range in the Amazon basin, with records from nine countries, from Bolivia and Peru to the Guianas and Venezuela.

The species is common in captivity and is considered relatively easy to keep and breed. It does need a lot of space, high humidity, warm temperatures similar to its rainforest home and regular cleaning of its enclosure. In captivity it eats an all-insect diet.

Other frogs with pages here include the tomato frog and the poison dart frogs.