Overview

Frogs are tailless amphibians that belong to the order Anura and are familiar members of freshwater and terrestrial ecosystems. In everyday language the words "frog" and "toad" are often used to suggest differences in skin texture or habitat, but taxonomically they are part of the same broad group (Anura). What people call a toad typically shows a set of traits — thicker, drier skin and a more terrestrial life — that represent an adaptation to drier habitats, rather than a separate, single lineage. The toad-like body plan has evolved multiple times, an example of convergent evolution.

Anatomy and life cycle

Most frogs are adapted to both land and freshwater environments, though they do not tolerate saline seas. Their life history features metamorphosis, a dramatic transformation from aquatic larvae to air-breathing adults. Females lay eggs in water or damp places; these eggs are commonly called frogspawn and hatch into tadpoles. Tadpoles generally have tails and gills for aquatic respiration. As development proceeds a tadpole forms limbs and lungs; the intermediate "froglet" still shows a residual tail, and the mature adult has powerful hind legs and no tail.

Adult frogs have several characteristic features: long hind limbs for jumping, eyes positioned for a wide field of view, and a sticky tongue that many species use to capture insects and other small prey. Most frogs vocalize; the familiar croak is produced by passing air over vocal cords while inflating the throat sac. Some species are arboreal and live in trees, using adhesive pads on their toes to climb (tree-dwelling species), while others have evolved chemical defenses and are poisonous to predators.

Habitat, ecological roles, and impacts

Frogs occupy a wide range of habitats from tropical rainforests to temperate ponds and seasonal wetlands. They serve several ecological functions: as predators of arthropods and other small animals, as prey for birds, mammals and reptiles, and as nutrient movers between aquatic and terrestrial systems. Because they are sensitive to changes in water quality, temperature and pollution, frogs are often used as indicators of environmental health. When an introduced amphibian appears outside its native range it can alter the local ecosystem, competing with native species or spreading disease.

  • Typical diets: insectivorous species that control pest populations.
  • Ecosystem services: nutrient cycling and food-web connections.
  • Vulnerabilities: dependence on freshwater for reproduction and permeable skin that absorbs contaminants.

Human uses and cultural notes

People have interacted with frogs in many ways: they appear in folklore and art, are studied in biology and medicine, and are consumed in some cuisines. For example, frog legs are eaten in parts of France, China, and some regions of the United States Midwest. Collecting and trade can affect local populations, and where frogs are removed on a large scale there can be knock-on effects on food webs, especially where frogs are significant predators of insects.

Classification and conservation

Frogs are members of the modern amphibian group Lissamphibia, the only surviving class of amphibia. Many frog species are declining worldwide due to habitat destruction, pollution, climate change and emerging diseases such as chytridiomycosis. Conservation efforts include habitat protection, captive breeding and disease management. Because frogs link aquatic and terrestrial habitats and respond quickly to environmental stress, they remain a focus for scientific research and conservation planning.

Understanding frog biology and respecting local regulations concerning collection and trade can help preserve their ecological roles and the diversity of species that continue to fascinate scientists, naturalists and the public.