# Tree Frog — Facts, Threats & Conservation

*Family Hylidae (Rafinesque, 1815) and related arboreal families — over 800 species*

> Tree frogs are over 800 species of arboreal frogs, mainly in the family Hylidae, that climb using adhesive toe pads which work by wet adhesion — a thin layer of mucus creating surface tension against the surface rather than suction.

**IUCN status:** Varies by species — many Least Concern, some Critically Endangered  ·  **WARN range:** The Americas, Europe, Asia, Australia

## Quick facts
| Fact | Value |
| --- | --- |
| Length | 2–14 cm depending on species |
| Adhesion mechanism | Wet adhesion — surface tension, not suction |
| Best-known species | Red-eyed tree frog (Agalychnis callidryas) |
| Defence | Camouflage at rest, deimatic startle display when disturbed |
| Egg laying | Often on leaves overhanging water, so tadpoles drop in |
| Main threats | Habitat loss, chytrid fungus, climate change |

## Scientific classification
- **Kingdom:** Animalia
- **Phylum:** Chordata
- **Class:** Amphibia
- **Order:** Anura
- **Family:** Hylidae, plus other arboreal families
- **Genus:** Hyla, Agalychnis, Litoria and many others
- **Species:** Over 800 described species

## Conservation status
- **Status:** Varies by species — Least Concern to Critically Endangered
- **Population:** Varies widely; many species have not been surveyed
- **Trend:** Decreasing for most assessed species
- **Assessed:** Varies
- **CITES:** Some species listed on Appendix II
- Chytrid fungus has affected over 500 amphibian species worldwide. Tree frogs' dependence on both forest and clean standing water means they are exposed to two habitat threats at once.

## Key facts: Tree Frog
- Tree frogs are not one taxonomic group. Arboreal life has evolved independently in several frog families across the Americas, Europe, Asia and Australia.
- Their toe pads work by wet adhesion, not suction. A thin layer of mucus creates surface tension between pad and surface, which is why a tree frog can climb wet glass but struggles on dry dust.
- The red-eyed tree frog's colours are a deimatic display — a startle response. At rest it is plain green; disturbed, it flashes red eyes and blue flanks to buy a moment to jump.
- Many species change colour, shifting between green and brown according to temperature, light and stress.
- Tree frog eggs are often laid on leaves overhanging water, so hatching tadpoles drop straight in. Some species' embryos can hatch early if they detect a predator attacking the clutch.
- Amphibians are the most threatened vertebrate class on Earth, with around 41% of assessed species at risk from habitat loss, chytrid fungus and climate change.

## How tree frogs stick to glass
The mechanism is not suction, which is the common assumption. A tree frog's toe pad is covered in hexagonal epithelial cells separated by channels, and mucus glands keep a very thin fluid layer across the surface. Adhesion comes from surface tension in that layer — the same force that makes two wet glass slides hard to pull apart — combined with friction from close contact between the pad and the surface.

The channels between cells matter: they drain excess fluid so the layer stays thin enough to grip rather than becoming a lubricant. This is why tree frogs perform well on wet surfaces, where a suction cup would fail, and poorly on dry dusty ones. The design has been studied extensively by materials engineers working on reusable adhesives, and synthetic pads modelled on frog toes now exist in the laboratory.

## Why the red-eyed tree frog has red eyes
Agalychnis callidryas spends the day asleep on the underside of a leaf, legs tucked in, eyes closed, showing only uniform green. In that posture it is extremely difficult to see. The colours are entirely hidden.

When a predator disturbs it, the frog opens its eyes and leaps, exposing large red irises, blue-and-cream barred flanks and orange feet all at once. This is a deimatic display — a sudden change designed to startle rather than to intimidate. A snake or bird that hesitates for a fraction of a second loses the frog, and a fraction of a second is all the display needs to buy. It works because it is a surprise, which is also why the frog stays plain green the rest of the time.

## Eggs that hatch early to escape
Red-eyed tree frogs and several relatives lay eggs in gelatinous clutches on leaves overhanging ponds. Tadpoles normally hatch after about six or seven days and drop into the water below.

If a snake begins eating the clutch, the remaining embryos can hatch immediately — as early as four days — and drop out of reach. The embryos detect the specific pattern of vibration produced by an attacking predator and distinguish it from wind or rain, and hatching is triggered within seconds. It is one of the clearest documented cases of an embryo making an escape decision before birth, and it comes at a cost: early-hatched tadpoles are smaller and more vulnerable to aquatic predators. The embryo is trading one risk for another.

## What WARN does
WARN publishes free, sourced species education. Amphibians are the most threatened vertebrate class on Earth and among the least funded, so free accurate material on how they live and what is happening to them is a genuine gap worth filling.

If this guide helps you understand wildlife and the pressures it faces, a gift to WARN supports habitat protection and free public education in our partner countries.

## Frequently asked questions: Tree Frog
### How do tree frogs stick to surfaces?
By wet adhesion. Their toe pads secrete a thin layer of mucus that creates surface tension against the surface, and channels between the pad cells drain excess fluid so the layer stays thin enough to grip. It is not suction, which is why they climb wet glass easily.

### Why does the red-eyed tree frog have red eyes?
As a startle display. At rest the frog is plain green and hidden; when disturbed it opens its eyes and leaps, flashing red irises, blue flanks and orange feet. The sudden change buys the fraction of a second it needs to escape.

### Are tree frogs poisonous?
Most are not dangerously so. Many secrete mild skin toxins or irritants as a defence, and some Australian and South American species produce compounds of pharmacological interest, but tree frogs are not in the same category as poison dart frogs.

### How many species of tree frog are there?
Over 800. The family Hylidae alone contains more than 700 species, and other arboreal frog families across Africa, Asia and Australia have evolved similar adaptations independently.

### What do tree frogs eat?
Tree Frogs eat ~41% — Of assessed amphibian species are threatened with extinction. Tree frogs are over 800 species of arboreal frogs, mainly in the family Hylidae, that climb using adhesive toe pads which work by wet adhesion — a thin layer of mucus creating surface tension against the surface rather than suction.

### Where do tree frogs live?
Tree Frogs live in The Americas, Europe, Asia. Tree frogs are over 800 species of arboreal frogs, mainly in the family Hylidae, that climb using adhesive toe pads which work by wet adhesion — a thin layer of mucus creating surface tension against the surface rather than suction.

### Are tree frogs dangerous?
Tree Frogs are not generally dangerous to people. Tree frogs are over 800 species of arboreal frogs, mainly in the family Hylidae, that climb using adhesive toe pads which work by wet adhesion — a thin layer of mucus creating surface tension against the surface rather than suction. Give wild individuals space and do not corner or handle them.

### How long do tree frogs live?
A precise wild lifespan for tree frogs is not firmly established in the sources cited on this guide. Tree frogs are over 800 species of arboreal frogs, mainly in the family Hylidae, that climb using adhesive toe pads which work by wet adhesion — a thin layer of mucus creating surface tension against the surface rather than suction. Where longevity figures appear in the literature they vary by region, sex and whether animals are wild or captive.

### How big is a tree frog?
A Tree Frog is about 2–14 cm depending on species. Tree frogs are over 800 species of arboreal frogs, mainly in the family Hylidae, that climb using adhesive toe pads which work by wet adhesion — a thin layer of mucus creating surface tension against the surface rather than suction. Conservation status: Habitat loss, chytrid fungus, climate change.

## Sources
- [IUCN Red List — Agalychnis callidryas](https://www.iucnredlist.org/species/55290/112712952)
- [AmphibiaWeb — Hylidae](https://amphibiaweb.org/lists/Hylidae.shtml)

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Full guide: https://worldanimalrescuenetwork.org/wildlife-guides/tree-frog