The breeding behavior of frogs is one of their most distinctive characteristics. The annual occurrence takes place in freshwater, usually in still or slow-moving areas. Some species, however, have adapted sexual organs, such as enlarged testes that produce massive amounts of sperm, that enable fertilization to take place in rapidly flowing waters.
Frogs inhabit almost every part of the world and breed in a wide variety of areas. Since eggs can only develop in moist conditions, many frogs flock to temporary pools during their brief breeding seasons, but others reproduce in streams and water bodies that they always inhabit. Male frogs use mating calls to attract females, which can differentiate between their species and others based on the sound and location of the call. When a female reaches a calling mate, the male clasps her in a tight embrace, known as amplexus, in order to fertilize the eggs. The female then selects the site for egg deposition.
Although frogs are not generally aggressive, during breeding season they may become territorial and antagonistic. Males of many species will wrestle, kick, and bite in order to protect their calling areas. Moreover, some frogs that use boulders and other raised surfaces as calling sites may attempt to knock competitors into the surrounding waters. Males are the most frequent fighters, but female frogs, such as the Venezuelan Colostethus trinitatus, are also willing to exhibit aggressive behavior in order to protect egg-laying sites.