Frogs are members of the class Amphibia. They make up 85 percent of living species in this class and are widespread and successful on all continents except Antarctica. Frogs are cold-blooded vertebrate animals that lack scales, have squat bodies, long muscular hind legs, and typically lack tails. The word “amphibian” is derived from the Greek “amphi” and “bios” and translates into “double-life”. This refers to the fact that frogs return to the water to breed, develop, and the transform (or metamorphose) to live a mainly terrestrial existence.

True frogs lay their eggs (called spawn) in clumps that are smooth and damp. They also have teeth and strong, long webbed hind feet for leaping. True toads are also frogs. In general, toads have stockier bodies, rounder snouts, dry and warty skins, no teeth and move by walking. Toads also lay their spawn in long strings. The frogs that we most commonly call toads in Canada belong to the genus Bufo.

There are several striking changes during metamorphosis as tadpoles mature into frogs. The long gut of a tadpole, used to digest plants, shrinks in length and the intestines become shorter to prepare for a carnivorous diet on land as a frog. The mouth changes from a small oval opening to a wide structure with an extendible tongue attached to the front of the mouth. Initially, a tadpole uses tiny, external gills to breathe that are gradually replaced with internal gills. These internal gills are gradually replaced by lungs, which is why tadpoles gulp air from the water’s surface as they get older. Legs develop and the tadpole’s tail becomes smaller. It is completely absorbed once a frog’s metamorphosis is complete.

Most frogs only spend a small portion of their lives in the water and are not totally aquatic (with some exceptions, such as the Surinam toad, Pipa pipa, and the African clawed frog, Xenopus laevis). Many frogs do spend their lives in a moist environment, such as marshes, swamps, along a river, or in a forest. These moist environments are important because frogs lose water through their permeable skin.

Most frogs only spend a small portion of their lives in the water and are not totally aquatic (with some exceptions, such as the Surinam toad, Pipa pipa, and the African clawed frog, Xenopus laevis). Many frogs do spend their lives in a moist environment, such as marshes, swamps, along a river, or in a forest. These moist environments are important because frogs lose water through their permeable skin.

Frogs generally breed in water, be it a pond, lake, marsh or in puddles after a heavy rain. The eggs are commonly laid in water, although some eggs develop directly after being laid on land, in soil, beneath logs, in moss and bromeliads, or on leaves. Eggs laid on land are often well-camouflaged - the eggs of the New Guinean treefrog (Litoria iris), which spawns on green leaves, have green yolks.

External fertilization is the most common way frogs breed. The male frog arrives at the breeding place first and makes a distinctive call to attract females. When a female frog of the same species arrives, the male grabs her and wraps his forearms around her in a strong “hug” (a position known as amplexus). This pairing could last a few hours or even several days - the genus Atelopus are known to stay in amplexus for weeks or even months! After the paring, spawning begins. The female pushes the spawn mass out of her body by pressing her abdomen and the male spreads his sperm over the exiting egg clump. He releases his grip once the spawning is complete. There are exceptions to the common external fertilization method. For example, the tailed frog, Ascaphus truei fertilizes its eggs internally before they are laid. There are also frogs that give birth to live young.

By producing lots of eggs, there is a better chance of the species surviving. Only one in five eggs matures into a frog, so frogs produce hundreds of eggs so there will be mature frogs to breed and ensure the continuation of the species.

Frogs vary greatly in natural colours, from the bright green White’s tree frog (Litoria caerulea) to the blue poison dart frog (Dendrobates azureus). Frogs use their bright colours as a warning to predators, for species recognition or for attracting a mate. Bright colours can also indicate that a frog is poisonous. Some frogs, such as the gray treefrog (Hyla versicolor), can even adjust their colour according to changes in light, moisture, chemicals or temperature.

Frogs have many predators, including newts, fishes, snakes and aquatic insects. Aquatic birds also enjoy eating frog embryos and tadpoles. Once frogs mature, they face predators such as snakes, bullfrogs, birds, fishes, turtles, crocodiles and mammals, including people.

Frogs are not very good at fighting, but they are excellent at hiding. They spend a lot of time beneath rocks, logs, in crevices or buried in the soil. They also have great camouflage, using both colour and texture to blend with their surroundings. Some frogs even have appendages to help alter their shape, such as the genus Hemiphractus, which have fleshy horns above their eyes. Frogs can leap away when provoked. Some will even emit a loud screech, while others play dead. Many frogs have some form of toxin, produced in their skin, to deter predators from eating them.

Most tadpoles eat algae, tiny pond creatures, and will scavenge dead organisms or vertebrates. Once on land, a frog becomes completely carnivorous, eating slugs, snails, worms, beetles, flies, moths, woodlice, small mammals and birds. Some frogs will eat other frogs.

Frogs have naked skin. That means frogs are vulnerable to chemicals and other changes in their environment—they are exposed to everything in water as well as on land. This makes the health of frogs in the wild a good indicator of our world’s health.

The worst problems that frogs face in the Lower Mainland include habitat loss through urban encroachment, agriculture, logging, mining, etc, as well as the introduction of species such as bullfrogs, green frogs and red-eared sliders (turtles) that eat or compete with them. Other threats include Pollution from pesticide and fertilizer use, automobiles etc., increases in ultra violet rays due to air pollution, and disease outbreaks.

Frogs are cold-blooded. When the temperature drops, a frog’s breathing gradually slows down until it “sleeps” at temperatures below 10ºC. When the temperature rises, the hibernation ends. Hibernating frogs frequently burrow in the soil, which could be at the bottom of a pond, under a log, or in a garden.