Red-eyed tree frog

Name and taxonomy

The species name callidryas joins the Greek kalos, meaning beautiful, with dryas, a nymph of the trees. English speakers also call it the red-eyed leaf frog or the gaudy leaf frog. In Spanish it is the rana de árbol de ojos rojos, and Maya speakers know it as yaaxmuch, the green frog. GBIF lists names in more than a dozen languages, from the German Rotaugenlaubfrosch to the Japanese akame amagaeru.

The genus Agalychnis belongs to the leaf frogs, Phyllomedusinae. Some authorities keep that group as a subfamily of the tree frog family Hylidae, and others raise it to the family Phyllomedusidae. The site fields follow the second view. Every Agalychnis species shares a red tint in the iris and a golden net pattern on the lower eyelid membrane. Like other tree frogs, it has a claw-shaped last bone in each toe. Wikidata records the IUCN status and the Spanish name rana arborícola under the same entry.

Evolution and relatives

Leaf frogs are a New World group of tree frogs that lay their eggs on leaves rather than in water. The red-eyed tree frog shares this habit with the rest of its genus. All Agalychnis species are climbers with long limbs and webbed toes, and all are active at night. Like the whole genus, this frog loses water fast in heat, which is probably why it hunts after dark.

Its colours are not a warning, because the skin carries no strong toxin. They may instead copy the colours of toxic frogs, a case of Batesian mimicry. The side stripes vary across the range: blue, blue and red, orange or purple in Costa Rica and Panama. The orange and purple forms are not genetically distinct groups, so distance and drift may explain them. The skin reflects strongly in the near infrared, unlike that of the European tree frog. That reflectance may help the frog match a leaf to a predator that sees beyond the visible range.

Appearance

The back is bright leaf green and the belly is pale blue or cream. Blue and yellow bars run along the flanks and the inner legs. The feet are orange, webbed, and tipped with round pads that grip the underside of a leaf. The skin is smooth with few or no bumps, and a mucus gland on the surface slows water loss and resists infection.

The eyes are large and red with a vertical pupil. There is no true eyelid, only a clear membrane that lets light through when the eye is shut. That is thought to let a sleeping frog wake when a shadow passes over it. Adults measure 4 to 7 centimetres and weigh about 6 to 15 grams. Males reach about 51 millimetres, and females grow to about 76 mm.

A tadpole is fairly large, 4 to 5 centimetres, with a long narrow tail and pale grey skin. A froglet has a green torso and yellow eyes. The torso turns brown, then the eyes turn deep red as the frog matures. Young froglets can shift their skin colour with the time of day. The site fields describe the frog as green with blue and yellow sides and orange feet, which fits every source.

Habitat and range

The frog lives in the humid lowlands from southern Mexico through Central America to northern Colombia. Wikipedia gives a narrower core range, from north-eastern Honduras to Colombia. GBIF holds records from 10 countries, and most come from Costa Rica and Panama. iNaturalist holds 11,343 observations, which shows how often visitors meet it.

It needs rainforest or wet forest with a pond nearby, because the tadpoles must drop into water. It also lives in wetlands and in hill forest where cover and water remain. Humidity of at least 80 percent is usual in its haunts. It spends most of its life in the canopy among leaves. In hot or dry weather it drops lower and shelters under broad leaves near the floor. Records from the United States and Japan on GBIF are probably captive animals, not wild ones. The species has not been shown to travel far, and a frog probably stays near one pond for life.

Diet and hunting

The adult is a night hunter of insects. It takes moths, crickets, katydids, grasshoppers, flies and mosquitoes. Now and then it eats a smaller frog. Like other frogs, it probably waits for prey to move and then lunges with its sticky tongue.

Tadpoles feed in mid water on plants, algae, plankton, bacteria and dead matter. They also eat each other. After metamorphosis a froglet starts on fruit flies and pinhead crickets.

Carotenoids in the food matter a great deal. In the weeks after metamorphosis they speed female growth and raise the number of eggs she will lay. They also make the skin redder in both sexes. Captive frogs on a poor diet lose their colour. Keepers probably dust the insects with a carotenoid supplement for this reason.

Behaviour and social life

The frog is nocturnal. By day it presses itself flat on the underside of a leaf. It tucks its legs in, closes its eyes, and hides every colour but green. At dusk it wakes, climbs, and hunts.

When a predator finds it, the frog opens its eyes wide and stretches, which shows the red eyes, the blue flanks and the orange feet. The sudden colour startles the attacker for a moment, and the frog jumps. Biologists call this a deimatic or flash display. The trick probably works because the attacker has learned that bright colours can mean poison, even though this frog has none.

Frogs have been seen in groups, but nothing is known about any rank order among them. The species does not migrate. In the breeding season males fight each other, and a male shakes his branch to keep rivals away. Outside that season the frog is probably solitary, like most tree frogs.

Communication and senses

The male calls with a short chack, loudest when the rain is heaviest. Females judge a male by his call, his size and the stripe pattern on his flank. They prefer males whose stripes and calls match the local type. Call and colour also serve in territorial displays and against predators.

Males shake branches to send vibrations to rivals. This was the first evidence that a tree-living vertebrate communicates by vibration. The embryos sense vibration too, while still in the egg. They hatch early only when the pulses match the pattern of a snake or wasp attack, not a rainstorm. They also use light: embryos hatch towards the light, and clutches hatch just after nightfall.

The red eyes see well at night, and the closed membrane still lets light in. Animal Diversity Web notes that the flash of the eyes is itself a visual signal aimed at a predator. Like most frogs, it probably finds prey by sight and ignores an insect that does not move.

Reproduction and life cycle

Breeding follows the rains, from about October to March. Males call and wrestle for access to females. Larger males win more often, but pairs also tend to match in size, so that the male can fertilise the eggs. The female grips the underside of a leaf over a pond, and the winning male clasps her waist from behind in amplexus. She carries him for several hours while she lays.

A clutch holds about 40 eggs, and a female can lay several clutches in one night. The male fertilises them outside her body as they reach the leaf. Because there is no sperm priority, one clutch may have several fathers. The parents glue the eggs with sticky jelly and may fold the leaf over them. Then they leave, and neither returns. Animal Diversity Web gives a gestation of around 45 days, which probably covers the egg and early tadpole stages together.

Undisturbed eggs hatch in 6 to 8 days, and the tadpoles drop into the water below. A tadpole can live only about 20 hours on land, so a miss is fatal. The tadpoles stay in the water for weeks or months, depending on conditions, and then metamorphose. Young mature at about two years and breed two years after that. Wild frogs live about 5 years, and captive frogs average about 4.1 years but can pass 8.

Predators and threats

Each life stage has its own enemies. The wasp Polybia rejecta and the cat-eyed snake Leptodeira septentrionalis eat eggs. Shrimp of the genus Macrobrachium and the fish Brachyrhaphis rhabdophora take tadpoles, as do dragonflies and water beetles. Froglets and adults fall to water spiders, snakes, birds and bats.

The eggs fight back by hatching early. When a snake bites into a clutch, the whole clutch can hatch within seconds and scatter into the pond. Early hatching is a gamble, because a young tadpole is easier prey in the water. Drying eggs also hatch sooner than wet ones. A rainstorm or a flood can trigger the same response.

The larger threats are human. Logging and housing remove forest, and chytrid fungus threatens frogs everywhere. Ranavirus has killed wild tadpoles in die-offs. Populations in Costa Rica, Nicaragua and Panama are also caught for the pet trade.

Population and conservation

The IUCN lists the red-eyed tree frog as Least Concern, last assessed in 2016. It has a wide range, tolerates some change to its forest, and has a large captive population. Many local populations are falling all the same. The species sits on CITES Appendix II, which regulates trade.

Deforestation is the main cause of the decline. Parks across the range keep enough forest and ponds to hold the species. Captive husbandry and breeding improved a great deal in the 21st century, which eases pressure on wild frogs. No total population figure exists, and GBIF records are heavily skewed to Costa Rica. The IUCN reasoning rests partly on a captive population that is presumed large but not counted.

Relationship with humans

The frog is harmless to people. Its skin carries some active peptides that put off predators, but Animal Diversity Web records no harm to a person. It is a popular pet, and the trade in wild-caught frogs is a threat in three countries. Captive breeding now supplies much of the demand. Pet keepers seem to value it for its colour and for its calm habit of sleeping in full view on a leaf.

Like other amphibians, it absorbs pollutants through its skin, which makes it a useful early warning of a damaged environment. It is the poster animal of rainforest conservation campaigns. Its face appears on books, posters and tour brochures across Central America. Tourists in Costa Rica probably see this frog more than any other, given the GBIF and iNaturalist records.

In culture and myth

In Mesoamerica, frog calls announce the coming rains. The web notes link frogs to rain and fertility in Maya belief. The Maya name yaaxmuch simply means green frog, and it is still used in Yucatán. No named myth about this frog in particular appears in the sources read here.

In modern culture the frog stands for the rainforest itself. Conservation groups use its red eyes and green skin on campaign material. The species name means beautiful tree nymph, and the popular name gaudy leaf frog says the same in plain words. It is thought to be the most photographed frog in the world, though no source counts the pictures.