Types of Earthworms
Three ecological categories of earthworms - epigeics, anecics and endogeics, have been described. Each of these creates earthworm spheres with differing characteristics. The anecics and endogeics are known as soil ecosystem engineers and their impact on soils is great and may influence properties and processes at the ecosystem level. The functional role of epigeics is primarily that of litter transformers, like other litter invertebrates (Lavelle 1997).
Anecics (Greek for “up from the earth” or “out of the earth”)
Anecics the dominant earthworms (in biomass) in many temperate region soils, (Lavelle 1983) are primarily vertically burrowing species. They feed on surface litter and more or less are permanent refuges in underlying soil horizons. They often produce characteristic surface features called “middens” which are circular “mound-shaped” region around a surface of the burrow’s opening which is a mixture of surface organic materials (principally leaves) and soil. The feeding and casting habits of anecics may deeply influence soil characteristics up to >1m depth. Examples of Anecic earthworms include Lumbricus terrestris, Apporectodea longa.
Epigeics (Greek for “upon the earth”)
Epigeic species live in, consume, comminute and partially digest surface litter, rarely ingesting soil particles. Their mode of litter processing in natural systems results in greater nutrient leaching into the soil. Since epigeics feed purely on litter and generally have a short gut transit time they probably depend on a rapid response of gut microbes to aid in digestion. Epigeic earthworm guts preferentially stimulate some microorganisms, and reduce others leading to a relative dominance of microorganisms different to that found in uningested soils. Examples include Dendrobaena octaedra, D. attemsi, D. rubidus, Eiseniella tetraedra, Heliodrilus oculatus and Lumbricus rubellus.
Endogeics (Greek for “within the earth”)
Endogeics are the most prevalent earthworms (in biomass) in most tropical environments (Lavelle 1983) often being the only group present, particularly in agroecosystems. Endogeics are geophagous earthworms that feed on subsurface soil horizons and on soil OM of different qualities. They produce surface and below-ground casts of two main types: globular (compact, large) and granular (loose, small). Endogeic casts, with generally more clay and frequently more OM than uningested soil, contain and release significant amounts of nutrients and NH4 (Barois et al., 1999) than uningested soil. Examples include Allolobophora chlorotica, Apporectodea caliginosa, A. icterica, A.rosea, Murchieona muldali, Pontoscolex corethrurus and Lampito mauritii.