True frogs—the ones discussed in this article—belong to the family Ranidae. There are about 20 species in the United States and Canada, including the following:

With a body up to 8 inches (20 cm) long, this is the largest frog in North America and next to the largest in the world. The skin is green, brown, or black. The bullfrog is found in Canada, the eastern United States, and northern Mexico. Its deep, hoarse call is louder than that of any other species of frog. Bullfrogs are raised commercially for their legs, which are eaten fried or baked.

The bullfrog is Rana catesbeiana.

It is 2 to 4 inches (5 to 10 cm) long. The back is greenish-brown or bronze with numerous dark brown or gray spots; the belly is white. Ridges extend along the sides of the body. The green frog ranges from the Great Plains to the Atlantic, and from southern Canada to Mexico. The male's call is a low-pitched “Ctung! Ctung!”

The green frog is R. clamitans.

It is 2 to 3 1/2 inches (5 to 9 cm) long and is brown or green. Between the ridges that extend along the sides are two or three rows of dark spots. There is a light stripe on the upper jaw. The northern leopard frog is widely distributed over the northern United States and southern Canada. The male's call is a low snoring sound.

The northern leopard frog is R. pipiens.

It is 1 3/4 to 3 1/2 inches (4.5 to 9 cm) long. The skin is tan with two parallel rows of squarish spots down the back. The belly and hind legs are bright yellow or orange. The skin secretes a substance that is poisonous to predators. The pickerel frog inhabits swamps and meadows in the eastern United States. The male's call is a low croak.

The pickerel frog is R. palustris.

It is 3 to 5 1/2 inches (7.5 to 14 cm) long. The skin is olive green or black and has a rough texture. The male has a yellow throat. The skin secretes a substance that is poisonous to predators. The river frog inhabits swamps from South Carolina to central Florida. The male makes a grunting or snoring sound.

The river frog is R. heckscheri.

With a body only 1 1/2 to 2 3/4 inches (4 to 7 cm) long, it is one of the smallest frogs. The skin is tannish-pink with dark patches around the eyes and at the base of the forelegs. The wood frog is one of the first amphibians to appear in the spring. It inhabits moist woodlands in the northeastern United States and throughout Canada. The male makes a raspy quacking sound.

The wood frog is R. sylvatica.

In addition to coloration that camouflages them or warns that they’re poisonous, frogs have good eyesight. They also have a delicate sense of touch to help them keep track of their surroundings.

If a predator spots a frog, the frog might play dead because most predators prefer live food. If it’s too late to hide or play dead, a frog may try to scare its enemy and get away. For example, some tree frogs flash brilliant colors to startle their enemies. Budgett’s frog of Argentina and Paraguay bellows, screams, and grunts to scare foes away.

Frogs that live on the ground or in water have powerful legs that can help them hop or swim away from predators. Tree frogs can escape danger by leaping from branch to branch. Flying frogs don’t actually fly, but they can jump right out of trees and glide to safer places.

Frogs are helpful to humans in a number of ways. Frogs eat many insects that are pests, such as mosquitoes and flies. They also eat insects that harm crops.

In addition, because their bodies are so similar to the bodies of other vertebrates, students and scientists often study frogs. Recently, scientists learned that the chemicals some frogs secrete can be used in medicine to fight skin and eye infections.

Frogs are helpful in another way, too. Because they absorb water through their skin, they are often the first creatures to react to pollutants in the water. Frogs that get diseases or can no longer reproduce may give a warning to people about the harmful effects of pollutants in the environment.

Frogs can make good pets. They are colorful, and they are fun to watch as they grow.

But before you get a pet frog, find information at your library or talk to experts at a local pet store. Taking care of frogs can be a lot of work. Some frogs eat only live insects. And frogs can live a long time, so be prepared to care for a pet frog for many years. You should never release a store-bought frog into the wild. It may not be a native to your area, and so it could cause harm to the habitat.

A pet frog can be kept in a mesh- or screen-covered terrarium (tuh RAIR ee uhm), which is a transparent container made of glass or plastic. If your pet frog is a type that prefers a dry environment, small pebbles should be placed at the bottom of the container for drainage. Then potting soil and plants can be added. The completed terrarium should be placed in an area that is well lighted but out of direct sunlight.

In addition to frogs, terrariums can hold other amphibian pets, such as toads and salamanders. Pet terrariums need to be kept clean to prevent illness.