What is an endangered species? What is a threatened species? In fact there are many different definitions passed by different organisations and governments.

In the case of the United States of America, under the Endangered Species Act of 1973, "the term 'endangered species' means any species which is in danger of extinction throughout all or a significant portion of its range other than a species of the Class Insecta determined by the Secretary to constitute a pest whose protection under the provisions of this Act would present an overwhelming and overriding risk to man."A threatened species "means any species which is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range."

Every species no matter what kind and what size plays a crucial and important part in keeping other species alive. Take raisins and raspberries, for example. Grapevines in California are attacked by grape leafhoppers in whose eggs a species of wasp breeds. Because grape leafhoppers reproduce only once a year, the wasp, which must breed more often to survive, uses raspberry leafhopper eggs when grape leafhopper eggs are not around. In vineyards with raspberries and thus raspberry leafhoppers, grapevines rarely suffer much damage, because there are enough wasps to keep grape leafhopper numbers down. In vineyards without raspberries, and thus without the wasp, chemicals must be used to control grape leafhoppers, raising the cost of growing the grapes and producing raisins.

Lamb chops and scarab beetles are another example. Australian scarab beetles eat only the dung of native pouched mammals and not manure from sheep introduced by European settlers. So sheep ranchers must stock pastures with imported dung beetles to clear manure. Even desserts can depend on the unlikeliest creatures. Chocolate wouldn't exist without the tiny flies that pollinate cacao trees. Without fruits, there are no seed pods, and without seed pods, there is no chocolate.