Earthworms are invasive species throughout the world. Of a total of about 6,000 species of earthworm, about 120 species are widely distributed around the globe. These are the peregrine or cosmopolitan earthworms. Some of these are invasive species in many regions.
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Australia
Australia has 650 known species of native earthworm that survive in both rich and in nutrient-poor conditions where they may be sensitive to changes in the environment. Introduced species are commonly found in agricultural environments along with persistent natives. Most of the 75 or so exotics have been introduced accidentally. The total species numbers are predicted to exceed 2,000.
North America
A total of approximately 182 earthworm taxa in 12 families are reported from the United States and Canada, of which 60 (about 33%) are introduced. Only two genera of lumbricid earthworms are indigenous to North America while introduced genera have spread to areas without any native species, especially in the north where forest ecosystems rely on a large amount of undecayed leaf matter. When worms decompose that leaf layer, the ecology may shift making the habitat unsurvivable for certain species of trees, ferns and herbs. Larger earthworms such as the nightcrawler Lumbricus terrestris and the Alabama jumper, Amynthas agrestis, can be eaten by adult salamanders, which is beneficial for their populations, but they are too large for juvenile salamanders to consume, which leads to a net loss in salamander population.
Currently there is no economically feasible method for controlling invasive earthworms in forests. Earthworms normally spread slowly, but can be quickly introduced by human activities such as construction earthmoving, plantings, and the release of worms used as fishing bait.
United Kingdom
A recent threat to earthworm populations in the UK is the New Zealand flatworm (Arthurdendyus triangulatus), which feeds upon earthworms but has no local natural predator itself. Sightings of the New Zealand flatworm have been mainly localised, but it has spread extensively since its introduction in 1960 through contaminated soil and plant pots. Any sightings of the flatworm should be reported to the Scottish Crop Research Institute, which is monitoring its spread.