Wild animals, or nondomestic animals, are those which have not been domesticated or tamed but rather live in a natural state. Wild animals are not suited for interaction with humans, and even those that have been tamed have not, like their domestic counterparts, been bred selectively to fit into life with humans. Wild animals and plants together comprise wildlife; there are an estimated 5 million and 100 million species of wildlife on earth (The Millennium Ecosystem Assessment 2005 report notes that most estimates fall between 5 and 30 million). Currently scientists have identified and classified around 2 million species of animals, the vast majority of which are nondomestic animals. The large majority of these species are also invertebrates such as insects, mollusks, and crustaceans. Scientists estimate that there may be another 10 to 30 million unidentified species of insects alone.
Wild animals are found everywhere on earth, and in every ecosystem. Some ecosystems are more favorable for biodiversity (the number and variety of different life forms living in a particular biome or ecosystem or even planet); coral reefs are one of the most diverse ecosystems on earth, supporting more than 25% of all marine life. Jungles and rainforests are home to an estimated half of the world's plant and animal species; about 20% of the world's birds live in the Amazon rainforests.
Although wild animals exist everywhere, the destruction of their habitats is one of the main threats to biodiversity and to individual species. Tropical rainforests are deforested at an alarming rate, and regions such as the Arctic are threatened by climate change. Wild animals are also threatened by overkill (being hunted and fished faster than they can reproduce). Although the trapping and hunting of many exotic species is forbidden, a demand exists on the black market which keeps illegal hunters pursuing wild prey. Many countries and states ban the keeping of nondomestic animals as pets, but many wild animals are trapped and smuggled past the bans.
Scientists are constantly discovering new species of wild animals. Among those discovered in 2011, according to the International Institution for Species Exploration, are the Darwin's Bark Spider (whose silk is the toughest biological material to have been studied thus far) and the Walter's Duiker (a mammalian species first encountered at a wild meat market).