Epigeic Earthworms

Epigeic is Greek "for upon the earth."

Oligochaeta or earthworms of the annelida phylum are divided into 3 categories; anecic, endogeic, and the epegeic, depending on where they dwell relative to the Soil Horizons. Epegeic earthworms are defined as species that inhabit and feed at the soil surface.

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Description

Epegeic Earthworms are small bodied and range from 1-7 cm. Some are colored bright red, although most have a reddish brown skin pigmentation. The pigment is darker on the back, and lighter on the tail and the belly, which may provide extra protection from ultra violet rays.[1] Epegeics share basically the same anatomy and reproduction methods as the endgoic and anecic species.

Range, Habitat and Diet

They are adapted to live in moist conditions and variable temperatures at the soil surface. The worms found in compost piles are epigeic and are unlikely to survive in an environment of low organic matter.[2] Epegeics inhabit every continent except Anarctica, however they along with all other earthworms species are invasive in the previously earth worm free temperate and boreal forests of North America.[3] The endoeic species can turn epigeic during suitable weather conditions, but during drier weather retreat under the soil. Other epegeic migrate soil to aestivate or hibernate. Some classify earthworms with both these "migratory" type behaviors as epi-endogeics.

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Example Species

Dendrobaena octaedra []

Eiseniella tetraedra[]

Eudrilus eugeniae []

Lumbricus castaneus[]

Dendrobaena octaedra

Dendrobaena octaedra is a small (2-4 cm) epegeic with extensive morphological variability. This species has been introduced to the North American range, and demonstrates wide variability in somatic and reproductive characters in its native northern Europe range.[4] Dendrobaena octaedra is common in coniferous forests in its native European habitat along with its foreign North American range.[5]

Eudrilus eugeniae

Eudrilus eugeniae is frequently used in the vermicomposting of solid wastes. Similiar epegeic genera – Eisenia foetida and Perionyx excavatus are also able to speed up the decomposition process of organic matter particularly in tropical conditions.[6]

Lumbricus castaneus

This species is also known as the Chestnut Worm. The Castaneus is endemic to England and most active in the spring months.[7]

Eiseniella tetraedra

This red worm may vary from 2 to 8 cm in length. It is considered an aquatic species with a distinctive cliellum (saddle) around its segments. They are widespread in Britain and found year round in gardens, fields, pastures, forests, estuary flats, lake shores, manure, and other damp conditions.[8]

Ecological Impact

Benefits

Based on the feeding behavior of earthworms, epigeic species have a greater potential as waste decomposers, than anecics, and endogeics, due to their humus consumption and surface dwelling nature.[6] Epigeics are considered detrivores but will feed primarily on microorganisms associated with the decaying surface litter while facilitating the breakdown and mineralisation of that region.[9] These earthworms exert important effects on the presence of decomposer micro-organisms and their microbial grazers, which leads to changes in the rate of decomposition of the organic matter.[10] Nevertheless, little is known about whether and to what extent these changes are due to the direct effects of earthworms on the decaying material (i.e. transformations of the ingested material during passage through the gut) or to indirect effects related to their casting and burrowing activities.[11]

Subversive effects

Invasive earthworms are particularly problematic in previously earthworm-free temperate and boreal forests of North America that are dominated by Acer, Quercus, Betula, Pinus and Populus trees.[3] Epigeics physically disrupt the organic layer of the soil by consuming and mixing the F and H Soil Horizons layers, producing a homogenous and granular form of organic forest floor.[5] It has been shown that fungi and macroinvertabrate populations are altered in presence of epegeics.[1] Although some invasive epegeics change the dynamics of these forests they seem to have limited impact on the structure of the mineral soil and composition of the forest floor. The endoeic and anecic earthworms are found to have more deleterious effect on the forest floor and in turn the health of ecosystem with their extraordinary mixing of the Soil Horizons.[1][3]

References

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[1] Hale, Cindy. Earthworms of the Great Lakes. Kollath+Stensaas Pub., 2013.

[2] Edwards, Clive A. “Natural Resources Conservation Service.” Home | NRCS Soils, 2019, https://www.nrcs.usda.gov/wps/portal/nrcs/detailfull/soils/health/biology/?cid=nrcs142p2_053863

[3] Frelich, Lee E., et al. “Earthworm Invasion into Previously Earthworm-Free Temperate and Boreal Forests.” Biological Invasions Belowground: Earthworms as Invasive Species, 2006, pp. 35–45., doi:10.1007/978-1-4020-5429-7_5. https://link.springer.com/article/10.1007/s10530-006-9019-3

[4] Terhivuo, Juhani, and Anssi Saura. “Dispersal and Clonal Diversity of North-European Parthenogenetic Earthworms.” Biological Invasions Belowground: Earthworms as Invasive Species, 2006, pp. 5–18., doi:10.1007/978-1-4020-5429-7_2. https://link.springer.com/article/10.1007/s10530-006-9015-7

[5] Addison, J.a., and S.b. Holmes. “Effect of Two Commercial Formulations of Bacillusthuringiensis Suhsp. Kurstaki on the Forest Earthworm Dendrobaenaoctaedra.” Canadian Journal of Forest Research, vol. 26, no. 9, 1996, pp. 1594–1601., doi:10.1139/x26-179. https://www.nrcresearchpress.com/doi/abs/10.1139/x26-179#.XM0hFo5KjIU

[6] Singh, Arjun, et al. “Taxonomic and Functional Diversity of the Culturable Microbiomes of Epigeic Earthworms and Their Prospects in Agriculture.” Journal of Basic Microbiology, vol. 56, no. 9, 2016, pp. 1009–1020., doi:10.1002/jobm.201500779. https://onlinelibrary.wiley.com/doi/full/10.1002/jobm.201500779

[7]“Chestnut Worm (Lumbricus Castaneus).” INaturalist.org, https://www.inaturalist.org/taxa/484186-Lumbricus-castaneus

[8]“Eiseniella Tetraedra.” NatureSpot, 2019, https://www.naturespot.org.uk/

[9] Hendrix, Paul F., and Patrick J. Bohlen. “Exotic Earthworm Invasions in North America: Ecological and Policy Implications.” BioScience, vol. 52, no. 9, 2002, p. 801., doi:10.1641/0006-3568(2002)052[0801:eeiina]2.0.co;2. https://pdfs.semanticscholar.org/2540/a686a6cfa2f71fef74fd692182821583aa93.pdf

[10] Monroy, Fernando, et al. “Changes in Density of Nematodes, Protozoa and Total Coliforms after Transit through the Gut of Four Epigeic Earthworms (Oligochaeta).” Applied Soil Ecology, vol. 39, no. 2, 2008, pp. 127–132., doi:10.1016/j.apsoil.2007.11.011. https://www.researchgate.net/publication/222415275_Changes_in_density_of_nematodes_protozoa_and_total_coliforms_after_transit_through_the_gut_of_four_epigeic_earthworms_Oligochaeta

[11]Domínguez, Jorge, and María Gómez-Brandón. “The Influence of Earthworms on Nutrient Dynamics during the Process of Vermicomposting.” Waste Management & Research, vol. 31, no. 8, 2013, pp. 859–868., doi:10.1177/0734242x13497079. http://jdguez.webs.uvigo.es/wp-content/uploads/2013/07/the-influence-of-earthworms-on-nutrient-dynamics.pdf