U.S. Department of Agriculture: Animal and Plant Health Inspection Service


Document Type


Date of this Version

March 2003


Published by Encyclopedia of Pest Mnnagement.


Human beings have introduced other species around the world both accidentally and intentionally. Accidental introductions resulted from escape from captivity (monk parakeets [Myiopsitta monachus] in Florida), stowaways (rats [Ranus spp.] and house mice [Mus musculus] worldwide; brown tree snakes [Boiga irregularis] in Guam), or expansion of species' ranges. Intentional introductions occurred for various reasons including: 1) aesthetics (songbirds into Hawaii, grey squirrel [Sciurus carolinensis] into Europe, and European songbirds imported by British colonists into North America, Australia, and New Zealand); 2) economics (nutria [Myocastor coypus] introduced in the eastern US., and Arctic fox [Alopex lagopus] onto Aleutian Islands for development of fur industries); 3) recreation (pheasants [Phasianus colchicus] and cbukar [Afectoris chukar] introduced as game species from Asia to North America, and red deer [Cervus elaphus] introduced into New Zealand); 4) food (domestic livestock worldwide, rabbits [Oryetolagus cunniculus] into Australia, pigs [Sus scrofa] into Hawaii); 5) for biological control (mongooses [Herpestes auropunctatus] to control rats in Hawaii, fox [Vulpes vulpes] to control rabbits in Australia, and giant toad [Bufo marinus] to control cane beetles in Australia); or 6) releases from captive populations (bulbuls [Pycnonotus jocosus] in Florida and domestic ferrets [Mustela putorius] in California, mink [Mustela vison] and muskrat [Ondntra zibethicus in Europe, and horse [Equus caballus], donkey [Equus minus], and other ungulates into Australia and western North America). The majority of biological introductions fail. Of those that succeed, only a small fraction become serious pests. Many introductions, like livestock or pheasants into the US., have been generally beneficial; however, some introduced species become invasive, defined as nonnative species which cause substantial economic or ecological h m . The U.S. has at least 221 nonnative terrestrial vertebrate species[1] and New Zealand has 35 introduced birds and 33 mammals, where previously the only mammals consisted of 3 bats. [2] About 44 mammals have been introduced into Australia, of which 27 have become established, 13' along with 3 species of amphibians and reptiles and numerous birds. Ten species of terrestrial mammals on the Galapagos are aliens.