Frogs are animals that belong to a class called amphibia, which are cold-blooded animals with vertebrae. Frogs are characterised by bulging eyes, long webbed feet that allow them to swim and jump, and slimy skin. Baby frogs are known as tadpoles. They start to grow skin at about four weeks of age and legs at six to nine weeks. By about 12 to 16 weeks, they are fully developed into frogs.
Frogs have lived on the Earth for more than 200 million years, as long as dinosaurs. Frogs tend to live between four and 15 years, but those in captivity have been found to survive for 20 years. The largest frog, the goliath frog, can grow to 15 inches long and seven pounds in weight and is found in West Africa. At least 4,900 frogs have been found worldwide, and scientists believe that there are at least 1,000 that haven't been identified.
Frogs live on all continents except Antarctica, and different types of frogs can survive in differing climates because, as cold-blooded animals, they are able to adapt their body temperatures. There are no distinct patterns for frog habitats because they can live in the rainforests, mountains and the desert. Many tend to live out of the water and reproduce in streams or ponds. Where frogs live depends on factors such as temperature, vegetation, rainfall and the activity level of the frogs.
Two types of frogs that live in drier climates are the Catholic and flat-headed frogs. They survive by living underground in burrows or in the mud. The flat-headed frog is able to store water in its body. The Australian water-holding frog is able to live in burrows and survive up to seven years without water. Wood frogs are a type of frog that is able to live in cold-weather climates. These frogs live in areas above the Arctic Circle. They are able to break down glucose in their bodies and distribute it throughout their bodies. This glucose increases their tolerance to freezing. Along with these habitats, frogs also live in bog-like swamp, wetland, pond and river habitats.
Many frogs spend time in streams, especially those that are fresh water, because this is where they mate and spawn. The waters that they mate in can be flooded fields, wetland edges or streams. Female frogs lay clumps of eggs, often in calm and static water to keep them from getting moved around. Some tree frogs, in contrast, mate in tree branches over top of streams, and their eggs form into cocoon-like masses that fall safely down into the waters below. After tadpoles are born, they attach themselves to weeds and grasses in the streams in which they are born.
Frogs need to live in areas where they can find food, which for them are insects such as earthworms and spiders. They are able to catch their food using their tongues, which they move rapidly, and then eat their prey whole. They tend to hunt mostly at night. Since there are more insects in some places, such as tropical environments, more species of frogs tend to live in these areas.
Frogs have been able to adapt to their environments through camouflage. They have been able to develop colours that help them to hide from their predators such as snakes, lizard and birds. For example, the Budgett's frog is a brown colour and the Vietnamese mossy frog has bumps that allow it to blend in with moss and lichen. Poisonous frogs have also adapted a bright colouring that warns predators that they are dangerous.