Frogs and Toads: What Is a Frog?
Frogs and toads are amphibians. "Amphibian" comes from two Greek words meaning "a double life." Amphibians are born in water and spend most of their formative time in water. As they grow older, amphibians become land creatures, spending only a small amount of time in water.
Frogs and toads are so alike that most scientists do not make distinctions between them. However, there are ways to tell the difference between the two. Frogs usually have smoother, moister skin. True frogs are those that live both in and out of water. Aquatic frogs are slightly different; they are the ones who spend most, if not all, of their lives in water. Aquatic frogs have webbed toes. Frogs tend to lay their eggs in clusters. Frogs are usually leapers, covering good distances with powerful legs.
Toads usually have bumpier, drier, rougher skin. They live mainly on land. Toads do not have webbing between their toes. They lay their eggs in long chains. Toads are hoppers, going only short distances on stubby, heavy legs.
Frog Facts
Like dinosaurs, frogs are prehistoric. Scientists believe frogs began to evolve from water animals almost 200 million years ago. Today, there are about three thousand known species of frogs and toads.
Frogs live on all the world's continents except Antarctica. Frogs and toads can live in a variety of environments, from high mountains to the trees of a rain forest or the floor of the desert. Frogs are even found above the Arctic circle. They can exist in almost any habitat as long as fresh water is nearby.
The world's smallest frog is the Cuban pygmy frog which measures about one-half inch long when fully grown. The Goliath frog of West Central Africa is the largest. It can grow to more than a foot in length. The largest species of toad is South Africa's Blomberg's toad, which can be as large as a dinner plate. A common adult bullfrog's body measures from six to eight inches.
True frogs are found on the ground. They make their homes in moist dirt, in small piles of leaves, or anywhere close to a source of moisture. Aquatic frogs have webbed feet that help propel them when swimming. Most species of tree frogs have no webbing between their toes. Tree frogs have round sticky pads at the end of each toe that help grip wet leaves and slick branches.
Hot and Cold
Like all amphibians, frogs and toads are ectothermic, or cold-blooded, animals. This means they cannot keep their body temperature stable. Their body temperature reacts and changes depending on the outside temperature.
Frogs hibernate in cold weather. Some dig burrows in the ground or in the mud at the bottom of ponds to prepare for a long sleep. They hibernate until spring, when the temperature grows warmer. When it gets very cold, a frog's activity decreases. The North American wood frog survives for months in a frozen, deathlike condition. This frog turns the glucose, or sugar, in its body to a kind of antifreeze that concentrates in the frog's vital organs, saving them from damage while the rest of the frog freezes. Frogs have survived temperatures as low as 21 degrees Fahrenheit.
Desert frogs and toads go through a process called estivation, which is similar to hibernation. When the temperature becomes too hot, they burrow in the ground to sleep until things cool off.
In either case, the resting frog does not need to hunt or eat. Its body slows down or stops completely so the frog does not have to eat. When the ground around the frog returns to more normal temperatures, the frog wakes up. The frog then digs itself out and immediately starts looking for a meal.
Meat Eaters
Most of the world's frogs, including all North American frogs, are carnivores. Very few frogs are herbivores. Izecksohn's Brazilian tree frog in South America eats fruit. Another rare exception, the Bufo marinus toad, eats meat and some vegetation.
Carnivorous frogs eat small animals, such as invertebrates (which have no spine) like ants, termites, beetles, slugs, worms, and snails. They also eat flies, mosquitoes, small crustaceans, spiders, centipedes, and fish. Sometimes they eat slightly larger animals such as ducklings, snakes, baby turtles, bats, and mice. Larger frogs may also be cannibals and eat other frogs.
All prey is swallowed live and whole, then slowly digested within the frog's stomach. Since frogs swallow their prey whole, they can eat almost anything that will fit in their mouths.
Any Drinks with the Meal?
Although a frog eats a wide variety of prey, it never drinks. Moisture is absorbed through its skin by osmosis. Osmosis is one reason frogs stay near water. It is also why they shed their skin. When the skin becomes blocked with dirt or other substances, moisture or oxygen cannot pass through it. Without clean skin, a frog will die.
Some frogs can make do with very little water. The water-holding frog of Australia's deserts can live up to seven years without rain or new water. Inside its burrow, the frog surrounds itself in a sac of skin to seal in what little moisture is available.
Friend or Foe?
Frogs and toads benefit the environment. The majority of a toad's diet consists of insects and other pests. Gypsy moths, army worms, tent caterpillars, slugs, and other destructive creatures are all delicious to a toad. By eating insects and rodents, frogs keep the population of these pests low. However, not all toads are welcome guests.
When frogs or toads are introduced to a new environment, they may become a problem. When Australia imported the cane toad to help with their beetle population in the 1930s, it was a disaster. The toads were nocturnal, coming out only at night, while the beetles were active during the day. Since there were no beetles to eat at night, the toads quickly ate all sorts of other wildlife, including birds and snakes. There were no natural predators to keep the toads in check. They grew to an overwhelming number and still remain a problem today.
Even in their natural surroundings, a troop of frogs can cause problems. Preferred prey animals may be quickly reduced, or wiped out altogether, by large numbers of frogs all eating the same thing.