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| '''Earthworm''' is a common name referering to a segmented worm, phylum ], class ], order ]. There are over 2,200 species known worldwide, existing everywhere but Arctic and arid climates. They range in size from two centimeters (about one inch) to over three meters (eleven feet). A common type of earthworm is brownish red, with one thick band of flesh, and a total length of a few centimeters. | '''Earthworm''' is a common name referering to a segmented worm, phylum ], class ], order ]. There are over 2,200 species known worldwide, existing everywhere but Arctic and arid climates. They range in size from two centimeters (about one inch) to over three meters (eleven feet). A common type of earthworm is brownish red, with one thick band of flesh, and a total length of a few centimeters. | ||
| ⚫ | Earthworms live by burrowing underground in ] containing organic materials, which they help to decompose. The worm eats soil as it burrows. The 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 a gardener. | ||
| Earthworms are ]s, but cross-fertilize, and lay cocoons, from which small but otherwise adult earthworms are born. | Earthworms are ]s, but cross-fertilize, and lay cocoons, from which small but otherwise adult earthworms are born. | ||
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| One often sees earthworms come to the surface in large numbers after a rainstorm. They are not leaving the ground to escape drowning as the popular misconception holds, for earthworms do not drown easily. They come to the surface to mate. | One often sees earthworms come to the surface in large numbers after a rainstorm. They are not leaving the ground to escape drowning as the popular misconception holds, for earthworms do not drown easily. They come to the surface to mate. | ||
| ⚫ | Earthworms live by burrowing underground in ] containing organic materials, which they help to decompose. The worm eats soil as it burrows. The 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 a gardener. | ||
| The major benefits of earthworm activities to soil fertility can be summarised as; | |||
| * Biological; The earthworm is essential to composting; the process of converting dead organic matter into rich humus, a medium vital to the growth of healthy plants, and thus ensuring the continuance of the cycle of fertility. This is achieved by the worm's actions of pulling down below any organic matter deposited on the soil surface (eg, leaf fall, manure, etc) either for food or when it needs to plug it's burrow. Once in the burrow, the worm will shred the leaf and partially digest it, then mingle it with the earth by saturating it with intestinal secretions. Worm casts (see below) can contain 40% more humus than the top 6" of soil in which the worm is living. | |||
| * Chemical; As well as dead organic matter, the earthworm also ingests any other soil particles that are small enough (including stones up to one-twentieth of an inch across) into it's 'crop' wherein minute fragments of grit grind everything into a fine paste which is then digested in the stomach. When the worm excretes this in the form of casts which are deposited on the surface or deeper in the soil, a perfectly balanced selection of minerals and plant nutrients is made available in an accessible form. Investigations in the US show that fresh earthworm casts are 5 times richer in available nitrogen, 7 times richer in available phosphates and 11 times richer in available potash than the surrounding upper 6 inches of soil. In conditions where there is plenty of available humus, the weight of casts produced may be greater than | |||
| 4.5 kg (lOlb) per worm per year, in itself an indicator of why it pays the gardener or farmer to keep worm populations high. | |||
| * Physical; By it's burrowing actions the earthworm is of great value in keeping the soil structure open, creating a multitude of channels which allow the processes of both aeration and drainage to occur. ] co-founder] points out that by sliding in their tunnels, earthworms "act as an innumerable army of pistons pumping air in and out of the soils on a 24 hour cycle (more rapidly at night)" (''Permaculture- A Designer's Manual'', Tagari Press, 1988)- thus the earthworm not only creates passages for air and water to traverse, but is itself a vital component in the living biosystem that is healthy soil. | |||
| It is important that we do not take the humble earthworm for granted. Dr W E ] 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 carries up to 53,000 worms to the acre (131,000 per hectare), but more recent research from Rothamstead Experimental Station has produced figures suggesting that even poor soil may support 250,000 worms to the acre, whilst rich fertile farmland may have up to 1,750,000. 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 (6,200,000 per hectare), meaning that the weight of earthworms beneath the farmer's soil could be greater than that of his livestock upon it's surface. One thing is certain however. Rich, fertile soil that is cared for organically and well fed and husbanded by it's steward will reap it's reward in a healthy worm population, whilst denuded, overworked and eroded land will almost certainly contain little more than a few scrawny, undernourished specimens. | |||
| The application of chemical fertilisers, sprays and dusts can have a disastrous effect on earthworm populations. Nitrogenous fertilisers tend to create acid conditions, which are fatal to the worms, and often dead specimens are to be found on the surface following the application of substances like DDT, lime sulphur and lead arsenate. In Australia, the use of superphosphate on pastures almost totally wiped out the giant 9' Gippsland earthworm. | |||
| In addition, as earthworms are processors of large amounts of plant and mineral materials, even if not killed themselves they can accumulate pollutants such as DDT, lead, cadmium, and dioxins at levels up to 20 times higher than in the soil, which in turn are passed on at lethal dosages to the wildlife which feed upon them such as foxes, moles or birds. | |||
| Therefore, the most reliable way to maintain or increase the levels of worm population in the soil is to avoid the application of artificial chemicals, as well as adding organic matter, preferably as a surface mulch, on a regular basis. This will not only provide them with their food and nutrient requirements, but also creates the optimum conditions of heat (cooler in summer and warmer in winter) and moisture to stimulate their activity. | |||
| A recent threat to earthworm populations in the ]is the ] (Artiposthia triangulata), which feeds upon the earthworm, but in this country has no natural predator itself. At present sightings of the NZFW have been mainly localised, but this is no reason for complacency as it has spread extensively since it's introduction in 1960 through contaminated soil and plant pots. Any sightings of the flatworm should be reported to the Scottish Crop Research Institute, who are monitoring it's spread. | |||
| == External References == | == External References == | ||
Revision as of 20:48, 4 February 2003
Earthworm is a common name referering to a segmented worm, phylum Annelida, class Oligochaeta, order Opisthopora. There are over 2,200 species known worldwide, existing everywhere but Arctic and arid climates. They range in size from two centimeters (about one inch) to over three meters (eleven feet). A common type of earthworm is brownish red, with one thick band of flesh, and a total length of a few centimeters.
Earthworms are hermaphrodites, but cross-fertilize, and lay cocoons, from which small but otherwise adult earthworms are born.
Various species of earthworms are used in vermiculture, the practice of feeding organic waste to earthworms to decompose (digest) it, a form of composting by the use of worms.
One often sees earthworms come to the surface in large numbers after a rainstorm. They are not leaving the ground to escape drowning as the popular misconception holds, for earthworms do not drown easily. They come to the surface to mate.
Earthworms live by burrowing underground in soil containing organic materials, which they help to decompose. The worm eats soil as it burrows. The 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 a gardener.
The major benefits of earthworm activities to soil fertility can be summarised as;
- Biological; The earthworm is essential to composting; the process of converting dead organic matter into rich humus, a medium vital to the growth of healthy plants, and thus ensuring the continuance of the cycle of fertility. This is achieved by the worm's actions of pulling down below any organic matter deposited on the soil surface (eg, leaf fall, manure, etc) either for food or when it needs to plug it's burrow. Once in the burrow, the worm will shred the leaf and partially digest it, then mingle it with the earth by saturating it with intestinal secretions. Worm casts (see below) can contain 40% more humus than the top 6" of soil in which the worm is living.
- Chemical; As well as dead organic matter, the earthworm also ingests any other soil particles that are small enough (including stones up to one-twentieth of an inch across) into it's 'crop' wherein minute fragments of grit grind everything into a fine paste which is then digested in the stomach. When the worm excretes this in the form of casts which are deposited on the surface or deeper in the soil, a perfectly balanced selection of minerals and plant nutrients is made available in an accessible form. Investigations in the US show that fresh earthworm casts are 5 times richer in available nitrogen, 7 times richer in available phosphates and 11 times richer in available potash than the surrounding upper 6 inches of soil. In conditions where there is plenty of available humus, the weight of casts produced may be greater than
4.5 kg (lOlb) per worm per year, in itself an indicator of why it pays the gardener or farmer to keep worm populations high.
- Physical; By it's burrowing actions the earthworm is of great value in keeping the soil structure open, creating a multitude of channels which allow the processes of both aeration and drainage to occur. Permaculture co-founderBill Mollison points out that by sliding in their tunnels, earthworms "act as an innumerable army of pistons pumping air in and out of the soils on a 24 hour cycle (more rapidly at night)" (Permaculture- A Designer's Manual, Tagari Press, 1988)- thus the earthworm not only creates passages for air and water to traverse, but is itself a vital component in the living biosystem that is healthy soil.
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 carries up to 53,000 worms to the acre (131,000 per hectare), but more recent research from Rothamstead Experimental Station has produced figures suggesting that even poor soil may support 250,000 worms to the acre, whilst rich fertile farmland may have up to 1,750,000. 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 (6,200,000 per hectare), meaning that the weight of earthworms beneath the farmer's soil could be greater than that of his livestock upon it's surface. One thing is certain however. Rich, fertile soil that is cared for organically and well fed and husbanded by it's steward will reap it's reward in a healthy worm population, whilst denuded, overworked and eroded land will almost certainly contain little more than a few scrawny, undernourished specimens.
The application of chemical fertilisers, sprays and dusts can have a disastrous effect on earthworm populations. Nitrogenous fertilisers tend to create acid conditions, which are fatal to the worms, and often dead specimens are to be found on the surface following the application of substances like DDT, lime sulphur and lead arsenate. In Australia, the use of superphosphate on pastures almost totally wiped out the giant 9' Gippsland earthworm. In addition, as earthworms are processors of large amounts of plant and mineral materials, even if not killed themselves they can accumulate pollutants such as DDT, lead, cadmium, and dioxins at levels up to 20 times higher than in the soil, which in turn are passed on at lethal dosages to the wildlife which feed upon them such as foxes, moles or birds. Therefore, the most reliable way to maintain or increase the levels of worm population in the soil is to avoid the application of artificial chemicals, as well as adding organic matter, preferably as a surface mulch, on a regular basis. This will not only provide them with their food and nutrient requirements, but also creates the optimum conditions of heat (cooler in summer and warmer in winter) and moisture to stimulate their activity.
A recent threat to earthworm populations in the UKis the New Zealand Flatworm (Artiposthia triangulata), which feeds upon the earthworm, but in this country has no natural predator itself. At present sightings of the NZFW have been mainly localised, but this is no reason for complacency as it has spread extensively since it's introduction in 1960 through contaminated soil and plant pots. Any sightings of the flatworm should be reported to the Scottish Crop Research Institute, who are monitoring it's spread.