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Earthworm

Earthworm is the common name for the larger members of the Oligochaeta Oligochaeta

The Oligochaeta are well-segmented Annelid [i]s, most with a spacious coelom [i] that is us ... 

  in the phylum Annelida Annelid

The annelids, collectively called Annelida , are a large phylum [i] of animal [i] ... 

. In classical systems they were placed in the order Opisthopora, on the basis of the male pores opening to the outside of body posterior to the female pores, even though the male segments are anterior to the female. Cladistic Cladistics

Cladistics is a branch of biology [i] that determines the evolution [i]ary relationships between organis ... 

 studies have supported placing them instead in the suborder Lumbricina of the order Haplotaxida. Folk names for earthworm include "dew-worm", "night crawler" and "angleworm". Earthworms are also called megadriles , as opposed to the microdriles, which include the families Tubificidae, Lumbriculidae, and Enchytraeidae, among others.

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Encyclopedia

Earthworm is the common name for the larger members of the Oligochaeta Oligochaeta

The Oligochaeta are well-segmented Annelid [i]s, most with a spacious coelom [i] that is us ... 

  in the phylum Annelida Annelid

The annelids, collectively called Annelida , are a large phylum [i] of animal [i] ... 

. In classical systems they were placed in the order Opisthopora, on the basis of the male pores opening to the outside of body posterior to the female pores, even though the male segments are anterior to the female. Cladistic Cladistics

Cladistics is a branch of biology [i] that determines the evolution [i]ary relationships between organis ... 

 studies have supported placing them instead in the suborder Lumbricina of the order Haplotaxida. Folk names for earthworm include "dew-worm", "night crawler" and "angleworm".

Earthworms are also called megadriles , as opposed to the microdriles, which include the families Tubificidae, Lumbriculidae, and Enchytraeidae, among others. The megadriles are characterized by having a multilayered clitellum Clitellum

In earthworm [i]s and some other annelids [i], the Clitellum is a thickened gland [i]ular section of the ... 

 , a vascular system with true capillaries, and male pores behind the female pores.

Overview


There are over 5,500 named species known worldwide, existing everywhere but Polar and arid climate Climate

The climate is commonly considered to be the weather [i] averaged over a long period of time, typically ... 

s. They range in size from two centimeters to over three meters in the Giant Gippsland Earthworm. Amongst the main earthworm species commonly found in temperate regions are the reddish coloured, deep-burrowing Lumbricus terrestris Lumbricus terrestris

Lumbricus terrestris is a large reddish worm native to Europe [i], but now also widely distributed e ... 

,

In temperate zone areas, the most commonly seen earthworms are lumbricids , mostly due to the recent rapid spread of a relatively small number of European species, but there are many other families, e.g. Megascolecidae, Octochaetidae, Sparganophilidae, Glossoscolecidae, etc.. These other families are often differ from the lumbricids in behavior, physiology and habitat.


Anatomy

Earthworms have a closed circulatory system Circulatory system

A circulatory system is an organ system [i] that moves substances to and from cells [i]; i ... 

. They have two main blood vessels that extend through the length of their body: a ventral blood vessel which leads the blood to the posterior end, and a dorsal blood vessel which leads to the anterior end. The dorsal vessel is contractile and pumps blood forward, where it is pumped into the ventral vessel by a series of "hearts" which vary in number in the different taxa. A typical lumbricid will have 5 pairs of hearts; a total of 10. The blood is distributed from the ventral vessel into capillaries on the body wall and other organs and into a vascular sinus in the gut wall where gases and nutrients are exchanged. This arrangement may be complicated in the various groups by suboesophageal, supraoesophageal, parietal and neural vessels, but the basic arrangement holds in all earthworms. Worms can make gurgling noise underground when disturbed, this comes from the worm moving through its lubricated tunnels as fast as it can.

Dissection

The classroom dissection Dissection

Dissection is usually the process of disassembling and observing something to determine its internal str... 

 of the earthworm and other animals has become controversial in recent years. One response to this has been the development of online virtual dissections.

Reproduction


Earthworms are hermaphrodite Hermaphrodite

[i] and [[female]... 

s but generally cannot fertilize their own eggs. They have testes, seminal vesicles and male pores which produce, store and release the sperm, and ovaries and ovipores. However, they also have one or more pairs of spermathecae that are internal sacs which receive and store sperm from the other worm in copulation. Copulation Mating

In biology [i], mating is the pairing of opposite-sex [i] or hermaphroditic [i] internal fertilization [i] ... 

 and reproduction Biological reproduction

Biological reproduction is the biological process [i] by which new individual organism [i]s are produced ... 

 are separate processes in earthworms. The mating pair overlap front ends ventral Anatomical terms of location

In human and zoological anatomy [i], several terms are used to describe the location of organ [i]s and o ... 

ly and each exchanges sperm with the other. The cocoon, or egg case, is secreted by the clitellum, the external glandular band which is near the front of the worm, but behind the spermathecae. Some indefinite time after copulation, long after the worms have separated, the clitellum secretes the cocoon which forms a ring around the worm. The worm then backs out of the ring, and as it does so, injects its own eggs and the other worm's sperm into it. As the worm slips out, the ends of the cocoon seal to form a vaguely lemon-shaped incubator in which the embryonic worms develop. They emerge as small, but fully formed earthworms, except for lacking the sexual structures, which develop later. Some earthworm species are mostly parthenogenetic Parthenogenesis

Parthenogenesis means the growth and development of an embryo [i] or seed [i] without fertilization [i] ... 

, in which case the male structures and spermathecae may become abnormal, or missing.

Regeneration

Earthworms have the facility to replace or replicate lost segments, but this ability varies between species and depends on the extent of the damage. Stephenson devoted a chapter of his great monograph to this topic, while G.E. Gates spent 10 years studying regeneration in a variety of species, but “because little interest was shown”, Gates only published a few of his findings that, nevertheless, show it is theoretically possible to grow two whole worms from a bisected specimen in certain species. Gates’s reports included:
  • Eisenia fetida with head regeneration, in an anterior direction, possible at each intersegmental level back to and including 23/24, while tails were regenerated at any levels behind 20/21.
  • Lumbricus terrestris Linneus, 1758 replacing anterior segments from as far back as 13/14 and 16/17 but tail regeneration was never found.
  • Perionyx excavatus Perrier, 1872 readily regenerated lost parts of the body, in an anterior direction from as far back as 17/18, and in a posterior direction as far forward as 20/21.
  • Lampito mauritii with regeneration in anterior direction at all levels back to 25/26 and tail regeneration from 30/31; head regeneration was sometimes believed to be caused by internal amputation resulting from Sarcophaga sp. larval infestation.


An unidentified Tasmanian native shown growing a second head is reported here: .

Behavior


Rainstorms

One often sees earthworms come to the surface in large numbers after a rainstorm. There are three theories for this behavior.

The first is that the waterlogged soil has insufficient oxygen for the worms, therefore, earthworms come to the surface to get the oxygen they need and breathe more easily. However, earthworms can survive underwater for several weeks if there is oxygen in it, so this theory is rejected by some.

Secondly, some species come to the surface to mate. This behavior is, however, limited to a few species.

Thirdly, the worms may be using the moist conditions on the surface to travel more quickly than they can underground, thus colonizing new areas more quickly. Since the relative humidity is higher during and after rain, they do not become dehydrated. This is a dangerous activity in the daytime, since earthworms die quickly when exposed to direct sunlight with its strong UV Ultraviolet

Ultraviolet light is electromagnetic radiation [i] with a wavelength [i] shorter than that of visible l ... 

 content, and are more vulnerable to predators such as birds Bird

Birds are biped [i]al, warm-blooded [i], oviparous [i] vertebrate [i] animals characterized [i] ... 

.


Locomotion and importance to soil

Earthworms travel underground by the means of waves of muscular contractions which alternately shorten and lengthen the body. The shortened part is anchored to the surrounding soil by tiny claw-like bristles set along its segmented length. The whole process is aided by the secretion of a slimy lubricating mucus. It was previously thought that in more compacted soils the earthworm actually eats its way through the soil, cutting a passage with its muscular pharynx and dragging the rest of the body along. However, the work of Kelly Dorgan has demonstrated that actually, worms turn their mouths inside out and form a wedge to crack dense soil, then move through the crack, expanding it as they go. This process aerates and mixes the soil, and is constructive to nutrient uptake by vegetation. In addition, earthworms often come to the surface and graze on the higher concentrations of organic matter present there, mixing it with the mineral soil. Because a high level of organic matter is associated with soil fertility, an abundance of earthworms is beneficial to the organic gardener Organic gardening

Organic gardening is a form of gardening [i] that uses substantial diversity in pest control [i] ... 

. In fact as long ago as 1881 Charles Darwin Charles Darwin

Charles Robert Darwin was an English [i] naturalist [i] who achieved lasting fa ... 

 wrote:

Benefits

The major benefits of earthworm activities to soil fertility can be summarized as:

  • Biological. The earthworm is essential to compost Compost

    Compost is the aerobically decomposed remnants of organic material [i]s . ... 

    ing; 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 either for food or when it needs to plug its 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 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 1/20 of an inch across—into its '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 United States

    The United States of America, also known as the United States, the U.S., the U.S.A., a... 

     show that fresh earthworm casts are 5 times richer in available nitrogen Nitrogen

    Nitrogen is a chemical element [i] which has the symbol N and atomic number [i] 7 in the periodic table [i] ... 

    , 7 times richer in available phosphate Phosphate

    In inorganic chemistry [i], a phosphate is a salt [i] of phosphoric acid [i]. ... 

    s and 11 times richer in available potash Potash

    Potash is an impure form of potassium carbonate [i] mixed with other potassium [i] salts. ... 

     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 per worm per year, in itself an indicator of why it pays the gardener or farmer to keep worm populations high.


  • Physical. By its 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 Permaculture

    Permaculture is a design system which aims to create sustainable [i] habitat [i]s by following ... 

     co-founder Bill 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 " . 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" , 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 Arable land

In geography [i], arable land is a form of agricultural [i] land use [i], meaning land [i] ... 

 contains up to 53,000 worms per acre , but more recent research from Rothamsted Experimental Station Rothamsted Experimental Station

The Rothamsted Experimental Station, one of the oldest agricultural research institutions [i] ... 

 has produced figures suggesting that even poor soil may support 250,000/acre , whilst rich fertile farmland may have up to 1,750,000/acre .

Professor I. L. Heiberg of State University of New York State University of New York

The State University of New York is a system of public institutions of higher education in New York [i], ... 

 College of Environmental Science and Forestry State University of New York College of Environmental Science and Forestry

The State University of New York College of Environmental Science and Forestry is a specialized doctoral... 

 has stated that in optimum conditions, the worm population may even reach 250,000,000 per acre , 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 fewer, scrawny, undernourished specimens.

Earthworms as invasives


North America

Lumbricid earthworms are not indigenous to North America and not only have displaced native earthworms in much of the continent, but have invaded areas where earthworms did not formerly exist. There are no native earthworms in much of North America, especially in the north, and the forests there developed relying on a large amount of undecayed leaf matter. The worms decompose that leaf layer, making the habitat unsurvivable for certain species of trees, ferns and wildflowers. Currently there is no economically feasible method for controlling earthworms in forests, besides preventing introductions. Earthworms normally spread slowly, but can be widely introduced by human activities such as construction earthmoving, or by fishermen releasing bait, or by plantings from other areas.

Soils which have been invaded by earthworms can be recognized by an absence of palatable leaf litter. For example, in a sugar maple Sugar Maple

The Sugar Maple Acer saccharum is a prominent tree [i] in the hardwood forests of eastern North America [i] ... 

 - white ash White Ash

The White Ash is one of the largest of the ash genus Fraxinus [i], growing to 35 m tall.... 

 - beech Beech

Beech is a genus of ten species [i] of deciduous [i] tree [i]s in the family Fagaceae [i], native to tem... 

 - northern red oak Northern Red Oak

The Northern Red Oak, Quercus rubra , is an oak [i] in the red oak [i] ... 

 association, only the beech and oak leaves will be seen on the forest floor , as earthworms quickly devour maple and ash leaves. Basswood Tilia

Tilia is a genus [i] of about 30 species of tree [i]s, native throughout most of the temperate Northern Hemisphere [i] ... 

, dogwood Dogwood

The Dogwoods comprise a group of 30-50 species of deciduous [i] woody plant [i]s in the family Cornaceae [i] ... 

, elm Elm

Elms are deciduous [i] and semi-deciduous [i] tree [i]s comprising the genus Ulmus, family Ulmaceae [i] ... 

, poplar Poplar

Populus is a genus of trees which includes the cottonwoods, poplars, and aspens, all of which are so... 

 and tuliptree Liriodendron

Liriodendron is a genus [i] in the magnolia [i] family consisting of two species of large deciduous [i]... 

 also produce palatable foliage.

Australia

Australia Australia

Australia, officially the Commonwealth of Australia, is a country in the Southern Hemisphere [i] c ... 

 has as estimated 300 species of earthworm. However, they generally survive only in nutrient-poor conditions, and are sensitive to changes in the environment. As a result, only introduced species are commonly found in agricultural environments. The introduction of earthworms has probably been accidental in Australia. There may be more than 500 different earthworm species in Australia now, including imported ones. However, only around 350 have been identified.

Special habitats

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 fetida lives in decaying plant matter and manure. Arctiostrotus vancouverensis from Vancouver Island Vancouver Island

Vancouver Island is located off Canada [i]'s Pacific [i] coast and is part of the Canadian province [i] ... 

 and the Olympic Peninsula Olympic Peninsula

The Olympic Peninsula is the large arm of land in western Washington [i] state that l ... 

 is generally found in decaying conifer logs or in extremely acid humus. Aporrectodea 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 Serpentine

Serpentine is a group of common rock-forming hydrous [i] magnesium [i] iron [i] phyllosilicate [i] ... 

 which have an earthworm fauna of their own.

Ecology


Earthworm populations depend on both physical and chemical properties of the soil, such as soil temperature, moisture, pH, salts, aeration and texture, as well as available food, and the ability of the species to reproduce and disperse.

One of the most important environmental factors is pH PH

pH is a measure of the acidity [i] of a solution [i], in terms of activity [i] of hydrogen [i] ... 

, but earthworms vary in their preferences. Most earthworms favor neutral to slightly acid soil. However, Lumbricus terrestris are still present in a pH of 5.4 and Dendrobaena octaedra at a pH of 4.3 and some Megascolecidae are present in extremely acid humic soils. Soil pH may also influence the numbers of worms that go into diapause. The more acid the soil, the sooner worms go into diapause, and remain in diapause the longest time at a pH of 6.4.

Earthworms form the base of many food chains. They are preyed upon by many species of bird Bird

Birds are biped [i]al, warm-blooded [i], oviparous [i] vertebrate [i] animals characterized [i] ... 

s, e.g. starling Starling

Starlings are small to medium-sized passerine [i] bird [i]s in the family [i] Sturnidae. ... 

s, thrushes, gull Gull

Gulls are seabird [i]s in the family Laridae. ... 

s, crow Crow

The true crows are in the genus [i] Corvus [i].... 

s, and robins. Mammals such as hedgehog Hedgehog

A hedgehog is any of the small spiny mammal [i]s of the subfamily [i] Erinaceinae and the order [i] ... 

s and moles eat many earthworms as well. Earthworms are also eaten by many invertebrates such as Ground beetle Ground beetle

Carabidae is a family within the insect order Coleoptera [i]. ... 

s and other beetle Beetle

Beetles are the most diverse group of insect [i]s. ... 

s, snail Snail

The name snail applies to most members of the mollusca [i]n class Gastropoda [i] that have coiled shell [i]... 

s, slug Slug

Slugs are gastropod [i] molluscs [i] without shells or with very small internal shells, in cont ... 

s and flatworm Flatworm

The flatworms are a phylum [i] of relatively simple soft-bodied invertebrate animal [i]s.... 

s. Earthworms have many internal parasites including Protozoa, Platyhelminthes, nematodes. They are found in many parts of earthworms' bodies such as blood, seminal vesicles, coelom, intestine, or in the cocoons.

Threats to earthworms


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 DDT

DDT was the first modern pesticide [i] and is arguably the best known organic pesticide. ... 

, lime sulphur and lead arsenate. In Australia Australia

Australia, officially the Commonwealth of Australia, is a country in the Southern Hemisphere [i] c ... 

, the use of superphosphate Superphosphate

Superphosphate is a fertilizer [i] produced by the action of concentrated sulfuric acid [i] on ground phosphate [i] ... 

 on pasture Pasture

Pasture is land with lush herb [i]aceous vegetation cover used for grazing of ungulate [i] livestock [i] ... 

s almost totally wiped out the giant 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 DDT

DDT was the first modern pesticide [i] and is arguably the best known organic pesticide. ... 

, lead Lead

Lead is a chemical element [i] in the periodic table [i] that has the symbol Pb and atomic number [i] ... 

, cadmium Cadmium

Cadmium is a chemical element [i] in the periodic table [i] that has the symbol Cd and atomic number [i] ... 

, and dioxin Dioxin

Dioxin is the popular name for the family of halogenated organic compounds [i], the most c ... 

s 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 fox Fox

A fox is a member of any of 27 species [i] of small omnivorous [i] canid [i]s. ... 

es, moles or bird Bird

Birds are biped [i]al, warm-blooded [i], oviparous [i] vertebrate [i] animals characterized [i] ... 

s.

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 and moisture to stimulate their activity.

A recent threat to earthworm populations in the UK United Kingdom

The United Kingdom of Great Britain and Northern Ireland is a country and sovereign state [i] tha ... 

 is the New Zealand Flatworm , 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 its 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 its spread.

Economic Impact


Various species of worms are used in vermiculture Vermicompost

Vermicompost is the end-product of the breakdown of organic matter [i] by some species [i] of earthworm [i] ... 

, the practice of feeding organic waste to earthworms to decompose it, a form of compost Compost

Compost is the aerobically decomposed remnants of organic material [i]s . ... 

ing by the use of worms. These are usually Eisenia fetida or the Brandling worm, also known as the Tiger worm or Red Wriggler, and are distinct from soil-dwelling earthworms.

Earthworms are sold all over the world. The earthworm market is sizeable. According to Doug Collicut , "In 1980, 370 million worms were exported from Canada, with a Canadian export value of $13 million and an American retail value of $54 million."

Earthworms are also sometimes sold as food for human consumption. Noke is a culinary term used by the Maori Maori

The word Maori refers to the indigenous people [i] of New Zealand [i] and to their language [i] ... 

 of New Zealand New Zealand

New Zealand is a country in the south-western Pacific Ocean [i] consisting of two large islands and many ... 

 to refer to earthworms which are considered delicacies.

Taxonomy and main geographic origins of earthworms


Main families :

  • Lumbricidae : temperate areas of Northern Hemisphere, mostly Eurasia
  • Hormogastridae : Europe
  • Sparganophilidae : North America
  • Almidae : Africa, South America
  • Megascolecidae : South East Asia, Australia and Oceania, western North America
  • Acanthodrilidae : Africa, southeastern North America, central and South America, Australia and Oceania
  • Ocnerodrilidae : Central and South America, Africa
  • Octochaetidae : Central America, India, New Zealand, Australia
  • Exxidae : Central America
  • Glossoscolecidae : central and Northern South America
  • Eudrilidae : Africa and South Africa

See also


  • Drilosphere
  • Lumbricidae
  • Megascolecidae
  • Sparganophilidae
  • Soil life Soil life

    Soil life or soil biota is a collective term for all the organisms living within the soil.... 

  • Gilbert White Gilbert White

    Gilbert White was a pioneering naturalist [i] and ornithologist [i].

... 


  • Noke

External links

  • Good for Composting and Fishing
  • Canadian worm awareness and appreciation site, with detailed worm anatomy.
  • Minnesota DNR information on the negative impacts of earthworms