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Most earthworms all over America, including the ubiquitous night crawler, are actually invasive species inadvertently imported from Europe by colonial settlers. These European immigrants have adapted well to the North American soil, often outcompeting native species for resources. Despite the threat posed by invasive species, at least 100 species of native earthworms in five families continue to live in North America.
The Komarekionidae family consists of a single species, the Kentucky earthworm (Komarekiona eatoni). This species has a limited distribution in the deciduous forests of the Appalachian mountains, from southern Pennsylvania into North Carolina and Tennessee in the south, and Southern Indiana and Illinois to the west. The IUCN considers the Kentucky earthworm a vulnerable species based on the fragmentation of existing populations and the declining quality of habitat in the region. Like other native species, Kentucky earthworms don't do well when people disturb their soil, for example by logging, providing exotic species the opportunity to take over and thrive.
Lumbricids are the most common worms in the United States, although most are not native species. Two genera in the Lumbricidae family include species endemic to North America, however: the Eisenoides genus and the Bimastos genus. The Eisenoides genus contains only two North American species, while there are 10 in the Bimastos genus. Bimastos earthworms live in rotting logs rather than in the soil like most earthworms, and perhaps not surprisingly are most often found in forests. Eisenoides earthworms live in moist bogs and forests throughout the eastern United States and Canada.
The Megascolecidae family of earthworms includes at least 76 species native to North America. The bulk of them, 46 species, are members of the Diplocardia genus. Of these, 42 live in the eastern United States from southern Pennsylvania into the Midwest and south to Florida, Texas and the Gulf Coast. Four Diplocardia earthworm species live on the Pacific coast. The 30 remaining Megascolecids are spread across 9 genera and live throughout the Pacific region. Included in these is the species Driloleirus macelfreshi. Native to the Pacific northwest, this species is the largest earthworm in North America, growing up to 3 feet in length.
Thirteen Sparganophilid species are native to North America, including two that live in northern California and Oregon. All the rest live throughout the Midwest, southern and eastern United States and into Ontario in Canada. These worms are semiaquatic, living in saturated soils both under waterways and along the banks of streams and rivers. Because of their need for moisture, no members of this family live in the desert or dry grassy plains of the Western or Southwestern United States.
The Louisiana mud worm (Lutodrilus multiresculatus) is the only species in the Lutodrilidae family. This semiaquatic worm has a limited distribution, occurring only in the state of Louisiana in mud flats and swampy areas between Baton Rouge and Bogalusa. The IUCN lists the Louisiana mud worm as near threatened. That's probably due to the creature's limited distribution, although monitors have historically listed the species as rare.
- American Institute of Biological Sciences: Exotic Earthworm Invasions in North America -- Ecological and Policy Implications
- Earthworm Ecology and Biogeography in North America; Paul F. Hendrix
- The New York Times: It's Natives vs. Newcomers Down in the Worm World
- United States Department of Agriculture: Native and Introduced Earthworms From Selected Chaparral, Woodland, and Riparian Zones in Southern California
- IUCN Red List: Lutodrilus Multivesiculatus (Louisiana Mud Worm)
- IUCN Red List: Komarekiona Eatoni (Kentucky Earthworm)
- Steve Mason/Photodisc/Getty Images