Frog

Frogs are short-bodied, tailless amphibians belonging to the order Anura, a name that comes from Ancient Greek and means 'without tail'. Adults have a stout body and protruding eyes, and most have long hind legs, no claws and a sticky tongue. Their skin is glandular and varies from dappled brown, grey and green to vivid red or yellow and black.

Size varies enormously. The smallest frog measures under 8 mm from snout to vent, while the largest, the goliath frog, reaches about 35 cm and around 3.3 kg.

The split between frogs and toads is informal. Rough, warty skinned types tend to be called toads, but this does not reflect true classification. The European fire-bellied toad, for example, is only slightly warty and prefers a watery habitat. Arboreal species such as White's tree frog (Litoria caerulea) have toe pads and only partly webbed toes.

Frogs are an ancient group. The oldest known fossil 'proto-frog', Triadobatrachus, comes from the Early Triassic of Madagascar, around 250 million years ago. It still had a tail and probably was not an efficient leaper.

The earliest true frogs in the anuran line lived in the Early Jurassic. Prosalirus had already lost nearly all of its tail and was well adapted for jumping. Modern frogs were probably fully evolved by the Jurassic period.

All tree-climbing lifestyles arose after about 66 million years ago, following the Cretaceous-Paleogene extinction event and the resurgence of forest that came afterwards. Frog fossils have been found on every continent.

Frogs are exceptional jumpers and, relative to size, the best of any vertebrate. The striped rocket frog can leap over two metres, more than fifty times its body length.

Males call to attract mates, and each species has its own call. Many calls are made with the mouth closed, while a higher-pitched distress call is made with the mouth open when a frog is grabbed. Tree frogs and some others also have a rain call made when humidity changes before a shower.

Frogs are cold-blooded, so they regulate temperature by moving into sun or shade. They squat close to the ground with hands and feet tucked in to cut water loss, and some become nocturnal to conserve water. Their distant vision is better than their near vision, and they can see in colour, even in low light. Most catch insects and other small prey with a sticky tongue and swallow them whole, often using their eyeballs to help push food down.

Frog skin is semi-permeable. It absorbs water and oxygen but also loses water easily, which makes frogs susceptible to dehydration. They produce large quantities of dilute urine. Skin glands give off mucus that helps protect against moulds and bacteria.

Skin is shed every few weeks. It usually splits down the back and belly, and the frog pulls its limbs free and eats the shed skin.

A serious fungal disease, chytridiomycosis, has spread around the world, and frog malformations are on the rise. Tadpoles that lose a leg to a predator may still grow into frogs that live a normal lifespan on three limbs.

This is general awareness only, not veterinary advice. Always consult a vet about your pet's health.

What is the difference between a frog and a toad?

The difference is informal and does not reflect classification. All members of the order Anura are frogs, and only the family Bufonidae are true toads. Toads generally have drier, warty skin and frogs smoother, moister skin, with many exceptions.

Do frogs have tails?

Adult frogs have no tail. Tadpoles have tails, and the tail regresses into an internal bone called the urostyle as they become adults.

What do frogs eat?

Adults generally eat small invertebrates, especially insects. A few species are omnivorous and a few eat plant matter. Tadpoles may be herbivorous, omnivorous or planktivorous.

Are frogs poisonous?

Their skin secretions range from distasteful to toxic. Bright red or yellow and black patterns often warn predators of toxicity.

Can frogs see in the dark?

Research shows that frogs can see in colour, even in very low light.

Do frogs breathe through their skin?

Yes. Oxygen can pass through their highly permeable skin, and they also breathe with lungs filled by buccal pumping.

Frogs make up around 88% of living amphibian species, with over 7,700 species in 59 families.

Their eyes can be pulled back through holes in the skull to help push food down the throat.

Frog tongues are coated in a fluid that turns runny under pressure and thick again afterwards, giving extra grip.

Arboreal frogs cling with toe pads that work by adhesion, not suction. Some high-canopy frogs have extensive webbing that lets them glide.

Some frogs, such as the wood frog, can survive being frozen, and a frozen frog can restart its heartbeat when it warms up.

A frog's skin colour can be darker in cool damp conditions than on a hot dry day.