Despite their dependence on environmental conditions, frogs live in many different surroundings, including water, semi-deserts, and mountains. The only conditions in which they cannot exist are salt water and the iciest and driest frontiers. Adult frogs rely on various methods of defense, including flight, poison, and many patterns and colors of camouflage. Frogs breathe and absorb water through their skin, which is periodically shed. Most are nocturnal or twilight animals, and rely more on their sense of vision and smell than hearing.
Many species hibernate through the winter months.
Almost all male frogs produce a noise amplified by vocal sacs on the floor of the mouth. Females are frequently somewhat larger than the male, but have a more limited and quieter repertoire of calls. Despite fairy tale claims, it has not yet been proven that frog-kissing produces princes. A group of frogs is called an army . The worldwide frog population has for some years been declining at unprecedented rates, causing speculation about the overall health of the biosystems from which they are disappearing.