Amphibians
Tree Frog
Hylidae · also called treefrog
A tree frog is a frog that has moved off the ground. It grips smooth leaves and bark with round sticky pads on its toes, spends the day pressed flat and green against a leaf, and hunts insects in the foliage at night. It is one of the most successful frog lifestyles, and it has evolved more than once.
Overview
Tree frog describes any small climbing frog with expanded toe pads, a type that has appeared in several families, chiefly the American and Australasian Hylidae (around 700 species) and the African and Asian Rhacophoridae. Tree frogs are usually small, big-eyed, and long-limbed, and most are green for camouflage. They eat insects and spiders at night and breed in still, fish-free water.
The pads, and the colours
The toe pads grip by wet adhesion — mucus spread over a micro-textured surface — letting a frog of a few grams hang under a leaf or climb glass. Many tree frogs change colour with temperature and mood, and some hide bright colours that they flash to startle a predator, the red-eyed tree frog being the famous case.
Eggs on a leaf
Several tree frogs glue their eggs to leaves over water, so the tadpoles drop in on hatching, and red-eyed tree frog embryos can hatch early if they sense a snake attacking the clutch.
Status
Tree frogs as a group are Not Evaluated. Many are common, but rainforest species are declining with deforestation, the European tree frog has vanished from much of its north-western range, and the chytrid fungus has hit several montane species.
Tree Frog: common questions
What makes a frog a tree frog?
A tree frog is defined by how it lives rather than by a single family tree. The key feature is the toe pad, an expanded, disc-shaped tip on each finger and toe that lets the frog cling to smooth vertical and overhanging surfaces. Alongside that, tree frogs tend to be small, slender, and long-limbed, with large forward-set eyes and a habit of resting flattened against a leaf by day and hunting in the foliage at night. This package has evolved independently in several frog groups, most importantly the New World and Australasian family Hylidae and the African and Asian family Rhacophoridae, so tree frog is a description of an ecological type as much as a taxonomic label.
How do tree frogs stick to leaves and glass?
By wet adhesion, not suction and not glue. The toe pad has a surface of tightly packed columnar cells separated by fine channels, kept wet by mucus the frog secretes. When the pad is pressed down, the thin film of fluid spread over that micro-textured surface creates adhesion at many small points, like a damp coaster stuck to a table, while the channels drain excess liquid so the pad does not simply slide off. The frog can also press the soft pad flat to increase the contact area and peel it up to release. The same principle lets a tree frog hang upside down from a leaf and even climb a pane of glass.
Why is the red-eyed tree frog so colourful if it needs to hide?
It hides and flashes at different moments. By day, a resting red-eyed tree frog tucks its limbs in, closes its eyes, and sits with only its bright green back showing, blending into a leaf. The vivid colours, the red eyes, the orange feet, and the blue-and-yellow bars on the flanks, are all normally hidden by the folded legs and shut eyelids. If a predator such as a bird or snake disturbs the sleeping frog, it suddenly opens its eyes and springs, and the burst of unexpected colour can make the predator hesitate or misjudge the leap, a trick called deimatic or startle display, giving the frog a fraction of a second to escape into the dark.
Are tree frogs good pets?
Some species are among the more forgiving amphibian pets, particularly White's tree frog, a large, placid, long-lived Australian species that tolerates handling better than most frogs, and the American green tree frog. They need a tall, planted, humid enclosure with climbing branches, gentle warmth, a shallow clean water dish, and a supply of appropriately sized live insects, and they should be handled only with clean, wet hands and rarely, since their skin absorbs whatever is on human hands. Wild-caught tree frogs, including many sold cheaply, often carry parasites and stress poorly, so captive-bred animals are strongly preferable, and it is important to check which species are legal to keep and never to release a pet frog.