Frogs and toads in U.S. zoos

Frogs, toads and how they live

All frogs and toads belong to one order, Anura, meaning "without tail". Adults have stout bodies, long hind legs, protruding eyes and a sticky tongue attached at the front of the mouth. The split between frogs and toads is informal: "toad" generally describes dry, warty-skinned land dwellers, and only the Bufonidae count as true toads. The Panamanian golden frog, despite its name, is one of them.

Most species lay eggs in water that hatch into tadpoles, which later metamorphose into adults. Frog skin is a working organ that can absorb water and oxygen, and that permeable skin is one reason frogs are treated as indicators of ecosystem health.

Color, toxins and calls

Skin glands make many frogs distasteful or toxic, and most toads have large parotoid glands behind the eyes. The cane toad, the largest true toad, is poisonous enough to be dangerous to dogs that bite it. Poison dart frogs advertise their toxins with bright colors; the blue poison dart frog and green-and-black poison dart frog are examples, and they get their toxins from the insects they eat.

Bright color does not always mean poison. The red-eyed tree frog is not poisonous; it rests with its eyes closed and legs tucked in, then flashes red eyes and orange feet to startle a predator. The Amazon milk frog defends itself by releasing a sticky white fluid.

Each species has its own call, made by pushing air through the larynx and often amplified by a vocal sac. The American bullfrog is named for the male's deep, bull-like call.

Conservation picture

Frogs are seen as environmental bellwethers, and their numbers have fallen sharply since the 1950s. More than a third of species are threatened with extinction. Chytridiomycosis, a fungal disease, has been linked to dramatic declines and extinctions, and it can kill every animal in some populations.

The Panamanian golden frog is Critically Endangered and may have been extinct in the wild since 2007, after chytrid reached its range; captive breeding is now its main safeguard. The Puerto Rican crested toad, Endangered on the IUCN Red List, is the focus of a captive breeding and reintroduction program that released a cumulative 260,000 tadpoles over two decades.

Introduced frogs can cause harm too. The cane toad is invasive in Australia, Florida and many Pacific islands, and the American bullfrog has been spread to more than 40 countries, where it outcompetes native frogs.