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The Earthworm travels underground by employing a combination of a series of tiny bristles ( setae) set along its segmented length and the secretion of a slimy lubricating mucous. The worm is thus able to propel itself forward by means of rippling muscular contractions, ingesting organic materials from even the heaviest soil as it burrows, which it helps to decompose.
The ingested soil is ground up, digested, and the waste deposited behind the worm. This process aerates and mixes the soil, and is often considered greatly helpful by gardeners and farmers. Because a high level of organic matter is associated with soil fertility, an abundance of earthworms is a happy sight for the organic gardener. In fact as long ago as 1881 Charles Darwin wrote;
"It may be doubted whether there are any other animals which have played so important a part in the history of the world, as have these lowly creatures"
Indeed, it is probably not much of an exaggeration to state that the humble earthworm is one of the most vital living creatures on the planet, for its actions are essential for the creation and vitality of soil, upon which almost all land plants and animals depend.
The major benefits of earthworm activities to soil fertility can be summarised as;
It is important that we do not take the humble earthworm for granted. Dr W E Shewell Cooper observed "tremendous numerical differences between adjacent gardens" (Soil, Humus And Health), and worm populations are affected by a host of environmental factors, many of which can be influenced by good management practices on the part of the gardener or farmer.
Darwin estimated that arable land contains up to 53,000 worms per acre (13/mē), but more recent research from Rothamstead Experimental Station has produced figures suggesting that even poor soil may support 250,000/acre (62/mē), whilst rich fertile farmland may have up to 1,750,000/acre (432/mē).
Professor I L Heiberg of New York College of Forestry has stated that in optimum conditions the worm population may even reach 250,000,000 per acre (62,000/mē), meaning that the weight of earthworms beneath the farmer's soil could be greater than that of his livestock upon its surface. One thing is certain however. Rich, fertile soil that is cared for organically and well fed and husbanded by its steward will reap its reward in a healthy worm population, whilst denuded, overworked and eroded land will almost certainly contain little more than a few scrawny, undernourished specimens.
While, as the name earthworm suggests, the main habitat of earthworms is in soil, the situation is more complicated than that. The brandling worm Eisenia foetida (or fetida) lives in decaying plant matter and manure. Arctiostrotus vancouverensis from Vancouver Island and the Olympic Peninsula is generally found in decaying conifer logs or in extremely acid humus. Alollobophora limicola and Sparganophilus and several others are found in mud in streams. Even in the soil species, there are special habitats, such as soils derived from serpentine which have an earthworm fauna of their own.
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