Earthworms as invasive species

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.^[1]^[2] Some of these are invasive species in many regions.

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. The total native species numbers are predicted to exceed 1,000.^[3]

Introduced species are commonly found in agricultural environments along with persistent natives. 66 exotic species are known by 1999, most of which have been introduced accidentally.^[3]

North America

Approximately 182 earthworm taxa in twelve families are reported from the United States and Canada, of which sixty (about 33%) are introduced.^[4] 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 L. rubellus and the Alabama (technically Asian) 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.^[5]

Currently there is no economically feasible method for controlling invasive earthworms in forests.^[6] 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

For the 69-70 known species,^[7] 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.

East Asia

In Taiwan, Pontoscolex corethrurus is known invasive with evidence of it displacing native worms. Eudrilus eugeniae has potential to do the same.^[8] For vermicompost, the native or naturalized Perionyx excavatus is recommended.^[9]

Control

At this point there is no known way to remove the earthworms from the soil, so proposals have focused on ways to slow their spread.^[10] One simple measure is to reduce the number of worms released during fishing practices. The Minnesota Department of Natural Resources, in cooperation with local groups, has launched a public education campaign using posters in bait shops and other outreach efforts.^[11]

The movement of dirt from one location to the other could also be regulated so that dirt from areas where earthworms are common is not moved into forests without the invasive species.^[12]^[11] To prevent the spread of invasive earthworms, it is recommended that people should only purchase compost or mulch that has been heated to appropriate temperatures and duration following protocols that reduce pathogens and kill the earthworm cocoons, or eggs.^[13]

In areas that have already been colonized, the number of worms can be reduced by removal of introduced shrubs such as common buckthorn (Rhamnus cathartica) and honeysuckle (e.g., Lonicera × bella), which produce leaf litter favored by worms.^[14] This may help mitigate negative impacts on the ecosystem.

Mustard pours can be used to survey for invasive worms at a site. A mustard pour can be created by mixing a gallon of water with one third cup of ground yellow mustard seed. Pouring the solution slowly over the soil will drive worms to the soil's surface without harming the plants.^[15] People with invasive worms on their property are advised not to move plants or soil from their property.

References

^ Cosmopolitan Earthworms
^ Plisko, J.D. 2010. Megadrile earthworm taxa introduced to South African soils (Oligochaeta: Acanthodrilidae, Eudrilidae, Glossoscolecidae, Lumbricidae, Megascolecidae, Ocnerodrilidae). African Invertebrates 51 (2): 289-312. Africaninvertebrates.org.za Archived 2012-03-12 at the Wayback Machine
^ ^a ^b Blakemore, Rob, Diversity of exotic earthworms in Australia - a status report. Transactions of the Royal Zoological Society of New South Wales, 1999 "Approximately 350 native species in about 30 genera are currently described for Australia, but an estimate of total number is about three times as large (Blakemore 1997a)."
^ Blakemore, R. 2006 American earthworms (Oligochaeta) from north of the Rio Grande.
^ Crawling to Oblivion, Scientific American, 300, 3 (March 2009), p. 22
^ "Great Lakes Worm Watch - What can I do?". University of Minnesota. 2011. Retrieved 31 January 2019.
^ Blakemore, R.J. 2008 http://www.annelida.net/earthworm/Britain%20&%20Ireland.pdf
^ "並非蚯蚓就是好外來蚯蚓大量混養引發生態衝擊" [Earthworms aren't all good; Exotic earthworms are mix-kept en masse, causing ecological shock]. 上下游News&Market (in Chinese (Taiwan)). 22 November 2016. Retrieved 22 May 2022.
^ "印度藍蚯蚓：你不知道養殖上有多好用的本土種——太平二號與牠們的產地（三）". PanSci 泛科學 (in Chinese (Taiwan)).
^ Lee E. Frelich, Cindy M. Hale, Stefan Scheu, Andrew R. Holdsworth, Liam Heneghan, Patrick J. Bohlen and Peter B. Reich. 2006. Earthworm invasion into previously earthworm-free temperate and boreal forests. Biological Invasions 8: 1235–245. doi:10.1007/s10530-006-9019-3
^ ^a ^b Callaham, Mac A. Jr.; González, Grizelle; Hale, Cynthia M.; Heneghan, Liam; Lachnicht, Sharon L.; Zou, Xiaoming (1 September 2006). "Policy and management responses to earthworm invasions in North America". Biological Invasions Belowground: Earthworms as Invasive Species (PDF). Vol. 8. pp. 1317–1329. doi:10.1007/978-1-4020-5429-7_11. ISBN 978-1-4020-5428-0. {{cite book}}: |journal= ignored (help)
^ Nico Eisenhauer, Stephan Partsch, Dennis Parkinson and Stefan Scheu. 2007. Invasion of a deciduous forest by earthworms: changes in soil chemistry, microflora, microarthropds, and vegetation. Soil Biology and Biochemistry 39: 1099-110.doi:10.1016/j.soilbio.2006.12.019
^ F., Hendrix, Paul; J., Bohlen, Patrick (2002-09-01). "Exotic Earthworm Invasions in North America: Ecological and Policy ImplicationsExpanding global commerce may be increasing the likelihood of exotic earthworm invasions, which could have negative implications for soil processes, other animal and plant species, and importation of certain pathogens". BioScience. 52 (9): 801. doi:10.1641/0006-3568(2002)052[0801:EEIINA]2.0.CO;2. ISSN 0006-3568.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ Madritch, Michael D.; Lindroth, Richard L. (13 May 2008). "Removal of invasive shrubs reduces exotic earthworm populations". Biol. Invasions. 11 (3): 663–671. doi:10.1007/s10530-008-9281-7. S2CID 26504134.
^ "Earthworm Sampling Methods". Great Lakes Worm Watch. University of Minnesota Duluth. Retrieved January 30, 2020.