| Oligochaeta
Native New Zealand earthworm.
Common name: earthworms.
Scientific name: phylum Annelida, class Oligochaeta. From Greek "oligos", few, and "chaite" , hair.
Description
Earthworms are the familiar red, reddish-brown, pink, pale, or sometimes greenish worms which are found in soil, forest litter, compost, and similar materials. The term "earthworm" applies to the larger members of the class Oligochaeta; the smaller, white, often microscopic soil oligochetes (family Enchytraeidae) are called pot worms. The body of an earthworm is circular or slightly flattened in cross-section, with visible annulations which correspond to the internal segments. The number of segments is very large - many hundreds in large species. On each segment of the body there are microscopic bristles, or setae, which the worm uses for grip as it moves through the substrate. The setae are hard to see, but can be felt on a live moving worm. Mature earthworms display a glandular ring or saddle - clitellum - on the front portion of the body. Clitellum has a function in reproduction, and its size, shape and position vary between species. The body size is variable. Some of the deep soil-dwelling native species can be more than 25 cm in length (the largest, Spenceriella gigantea from North Auckland, can reach 1.3 meters), while many smaller leaf litter-dwelling species are only few centimetres long. The colour of earthworms reflects their habitat: the deep-borrowing soil species are typically unpigmented (pale), while the species which live in the upper layers of leaf litter are dark - red or brown - in colour.
There are two major groups of earthworms in New Zealand. In all farmland, gardens, parks, city lawns, and pastures of New Zealand, the earthworm populations consist of a small group of introduced species, which belong to the family Lumbricidae. In native forests and tussock grasslands the native earthworms dominate, all of which belong to the family Megascolecidae.
Octolasion cyaneum, a common introduced earthworm.
Introduced Earthworms - Lumbricidae
Lumbricidae are the dominant earthworms of pastures and croplands of Europe. The New Zealand lumbricid worms are all of European origin, and were probably brought to New Zealand by early European settlers with soil on the roots of imported plants or in ship ballast. Lumbricidae since have become the dominant earthworms in all cultivated soils of New Zealand, with four species - Aporrectodea (= Allolobophora) caliginosa, A. trapezoides, Lumbricus rubellus, and Octolasion cyaneum - very widespread. These Lumbricidae are topsoil species and live in soil close to the surface, where they feed on dung, dead roots and other dead plant material.
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Te Ara - The Encyclopedia of New Zealand* on introduced earthworms:
"The most common introduced earthworms belong to the family Lumbricidae and, since such a large part of New Zealand has been cleared of the original vegetation and sown down to pasture, the lumbricid earthworms which feed on dead root and leaf material from pasture have become the dominant earthworm fauna both in pasture and in cultivated lands. They have been introduced at so many places and are so well acclimatised that there is no discernible relationship between their present distribution and geographical barriers as is the case with the native earthworms. The composition and population density of the lumbricid fauna is related directly to the level of fertility of the soil as modified by top-dressing and the composition of the pasture.
After the clearing of the land, native earthworms decline rapidly. The leaf-mould fauna is eliminated since there is no supply of leaf-mould; the topsoil fauna is usually eliminated but occasionally persists in a much reduced form; the subsoil fauna may be relatively unaffected but, if the soil is continually cultivated, this, too, fails to survive. There is an interval during which there is no further change in the condition of the depleted native fauna or during which earthworms are completely absent. The duration of this interval is related to the level of fertility of the soil and the availability of a population of lumbricid earthworms adjacent to the cleared land.
In the pumice land south of Rotorua, samples of the earthworm fauna were taken at various stages of development. Clearing of the land caused the extinction of the native earthworm Rhododrilus similis , and in pastures up to three years old no worms were found. As the pasture developed further and the "humus build up" at the surface became deeper, lumbricid species appeared. The first to appear was Octolasium cyaneum , a large sluggish species commonly found in the topsoil of low-fertility pastures on many soil types, the population being of the order of 100,000 per acre. After four or five years in pasture, Lumbricus rubellus then appeared and increased in numbers and, as the fertility of the pasture was built up, Allobophora calignosa and A. terrestris became established and dominated the earthworm fauna. In highly fertile pastures, numbers were of the order of 1-2 million per acre." |
* 'WORMS, EARTH', from An Encyclopaedia of New Zealand, edited by A. H. McLintock, originally published in 1966, updated 11-Jul-2005. Click here to read The Encyclopedia of New Zealand online.
The native subsoil species Octochaetus multiporus is bioluminescent. This species is found in the soil under native forests, tussock grasslands, and pastures.
Native earthworms - Megascolecidae Native earthworms of New Zealand are highly specialised inhabitants of forest soils. Only few species appear to be able to survive in open country habitats. There are three ecological groups of native worms - the leaf litter, topsoil, and subsoil species. The leaf litter species live within the layers of forest litter, where they feed on the decaying plant material. Topsoil species make burrows in the topsoil, but forage for food at or near the surface, in the leaf litter. Subsoil species inhabit organic-mineral zones of the soil and feed mainly on soil and dead roots. They make extensive burrows in the subsoil, ingesting the soil as they move along.
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Te Ara - The Encyclopedia of New Zealand* on native earthworms:
"Despite the limitations imposed by their environmental requirements, earthworms occupy a wide range of habitat but, as their name implies, have achieved their greatest success as soil-dwelling animals. The prolonged geographical isolation of New Zealand and the predominance of forest vegetation have resulted in the development of a forest-earthworm-fauna with species highly specialised to occupy particular ecological niches in particular types of forest, and there is an obvious stratification into leaf-mould, topsoil, and subsoil groups. The leaf-mould species are small, active, and heavily pigmented. The smallest is 15mm long and the largest 180 mm but most are between 20 mm and 50 mm. They do not make permanent burrows but move around freely in the loose material just as arthropods and other animals do; hence they are more prone to capture by predatory birds and are more frequently exposed to ultraviolet light than those species inhabiting topsoil or subsoil. Their ability to move quickly gives some protection from predators and their heavy and varicoloured pigmentation affords some protection from ultraviolet light and provides a degree of camouflage. Thirty-six species are found almost exclusively in leaf mould; most are confined to relatively small areas but at least four species (Diporochaeta obtusa, D. punctata, Neochaeta forsteri, Plagiochaeta sylvestris) are widely distributed. Both the topsoil and the subsoil dwellers have two distinct methods of making burrows in which to live. In the first method soil is swallowed and subsequently cast either at the soil surface or in natural cracks and cavities in the soil and in deserted burrows. In the second method the anterior end of the body is extended and inserted in spaces between the soil particles and then, by contracting the longitudinal muscles, the body is expanded laterally, compressing the soil to form a burrow. Usually burrowing consists of a combination of these two methods, the former predominating in more-compact soils and the latter in less-compact soils. As a burrow is formed it is lined with slime and thus has smooth walls firmly compacted by the lateral pressure applied during its construction.
The topsoil species are generally larger than leaf-mould species, the smallest is about 25 mm and the largest 300 mm but most are between 75 mm and 200 mm. They are not as heavily pigmented, nor do they move as rapidly as the leaf-mould species. In most species the body is circular in cross-section but in some (especially in Maoridrilus spp. and Neodrilus spp.) the body is almost square in cross-section with pairs of chaetae on the four corners and with thick body-wall muscle layers. Such species are generally the most active. Topsoil earthworms generally make shallow permanent burrows which they leave either at mating time or in order to forage for the food which they take back into their burrows. Most species appear to continue burrowing outside the confines of their living space and apparently live, to some extent at least, by ingesting soil and digesting the organic matter contained in it. Forty-eight native species are found almost exclusively in topsoil. A number of them found in tussock grassland areas (species of Rhododrilus in central North Island, and Maoridrilus in eastern South Island) are widely distributed, but most other topsoil species are confined to small areas.
Subsoil earthworms are usually large, sluggish, and unpigmented. The smallest is 32·5 mm and the largest 1,400 mm, but most are between 100 mm and 400 mm in length. The majority are circular in cross-section and have weakly developed body-wall muscles. They occasionally come to the surface or near to the surface for food, but otherwise are found only in the subsoil. They make very extensive burrows extending both laterally and vertically in the subsoil and occasionally going up into the topsoil. (Burrows of Spenceriella gigantea have been found about 20 mm in diameter and still continuing downwards at a depth of 11 ft 6 in.) They appear to make these burrows to obtain food by ingestion of soil and not primarily for shelter, like the burrows of the topsoil species. As they move forward they may deposit castings in the section of burrow left behind and it is not uncommon to find burrows partly filled with subsoil castings.
Earthworms are frequently found under logs and stones, under the bark of dead trees, in rotting logs, and in the litter of epiphytes in the axils of branches of trees. Most of these are species normally found in leaf-mould or topsoil and, more rarely, in subsoils, but one, Megascolides suteri , is found almost exclusively in rotting logs and is able to digest decaying fragments of wood. Ten species recorded from the Auckland Islands have all been found under logs and stones. Most of the ground is covered with acid peat (pH3·6-4·6) which is an undesirable habitat for these particular species." |
* 'WORMS, EARTH', from An Encyclopaedia of New Zealand, edited by A. H. McLintock, originally published in 1966, updated 11-Jul-2005. Click here to read The Encyclopedia of New Zealand online.
Notes on biology
The earthworms are hermaphrodites (each worm has both female and male organs), but they are not self-fertile and need a mate to reproduce . During mating, the earthworms exchange sperm, which is stored in the special receptacles called spermathecae. The fertilization itself occurs later in time during oviposition. During oviposition, the clitellum of an earthworm secretes a tube-like cocoon, which slides toward the anterior end of the worm. The eggs and sperm are deposited within the cocoon as it passes over the reproductive pores, so the fertilization is external. As the cocoon slips off the head of the worm, its ends close to form a smooth lemon-shaped capsule. These cream-colored, yellow, or brown cocoons can be often found in soil. The young earthworms resemble miniature adults, but lack reproductive organs and clitellum. Some earthworm species are parthenogenetic, in which case they do not mate and reproduce asexually.
Earthworms breathe and loose moisture by diffusion through the skin, and are therefore restricted to moist habitats. They are able to tolerate brief submersion in water, but during heavy rains Lumbricidae can be observed leaving their burrows and travelling over the surface. The exposure to sunlight is harmful to earthworms, particularly to the unpigmented deep-soil species.
Earthworms feed on dead and decaying plant fragments. Surface-dwelling species can feed on manure, compost, and similar organic materials. Some species are able to feed on decaying wood. The subsoil species are geophagous - they ingest large quantities of soil, and obtain the nutrients as the soil passes through their gut. There are few carnivorous species, but none of them occur in New Zealand.
The tiger worm, Eisenia fetida, can be occasionally found in the soil of New Zealand gardens. This worm lives in compost and manure, and can be brought into the soil with compost fertilizer. The earthworms are major decomposers in soil ecosystems, and have great beneficial effects on soil structure and fertility. Earthworms increase the efficiency of the nutrient turnover by speeding up the breakdown of dead roots, leaf litter, and other plant detritus. The introduced topsoil Lumbricidae are particularly important for soil quality of New Zealand pastures and gardens. Their burrowing increases soil porosity, and improves soil drainage and aeration. As they move through the soil, the worms mix the humus into deeper mineral soil horizons. In addition, after passing through the gut of an earthworm, the soil is enriched in nitrogen, phosphorus, potassium, and other essential plant nutrients. The amount of soil that passes through the digestive systems of lumbricid earthworms can be massive - up to 100 tonnes per hectare per year (Edwards and Lofty, 1972).
Distribution and conservation
Worldwide, there are currently around 2,500 described species of earthworms. The native fauna of New Zealand includes 173 species (27 genera), all from the family Megascolecidae. 14 genera are endemic to New Zealand. Many of the native earthworm species have restricted distribution within New Zealand, shaped by the geological history of the land. Megascolecidae in New Zealand inhabit the soil and litter of native forests and tussock grasslands, and most only survive in the areas that retained the undisturbed soil and native vegetation. The life cycles, distribution ranges, and environmental requirements of native earthworm species are not well known. Because any information is lacking for many of the native species, ca. 170 are listed as threatened or endangered on the NZ Department of Conservation threatened species list.
The earthworms, and particularly their cocoons, are easily transported with soil or on roots of plants, which may explain the global spread of several European Lumbricidae, which are now the most common earthworms in human-dominated environments of New Zealand and temperate zone worldwide. Currently, there are 16 introduced species of Lumbricidae in New Zealand, of which four species (A. caliginosa, A. trapezoides, L. rubellus, O. cyaneum) are widespread and abundant in all agricultural and urban soils. There are also five introduced Megascolecidae, but these are rare and only found in small isolated populations. Introduced earthworms are usually absent under native vegetation.
There is no evidence that introduced Lumbricidae actively displace native species. Rather, the destruction of the native earthworm fauna is the result of environmental changes following land conversion to pasture or cropland. When native forest is cleared, the native earthworms, particularly top-soil species, disappear rapidly, but it usually takes several years before the area is colonized by lumbricid earthworms. Only few native subsoil species - for example the deep burrowing Octochaetus multiporus, are able to adapt successfully to pastures.
Included images:
- Order Opisthopora
- Family Megascolecidae
- Octochaetus multiporus - Palmerston North, WI, North Island
- Unidentified species - Peel Forest Park, Dennistoun Bush, SC, South Island
- Unidentified species - Ohinetonga Scenic Reserve, TO, North Island
- Unidentified species - Rimu Valley Walk, SD, South Island
- Unidentified species - Bledisloe Park, Palmerston North, WI, North Island (2 images)
- Family Lumbricidae
- Octolasion cyaneum (Savigny, 1826)* - Palmerston North, WI, North Island
- Aporrectodea trapezoides (Dugés, 1828)* - Palmerston North, WI, North Island
- Unidentified species - Kaiteriteri Road, NN, South Island
- Order Tubificida
- Family Enchytraeidae
- Unidentified species - Westland National Park near Okarito, WD, South Island
- * - species exotic in NZ
Further information on New Zealand
earthworms:
Beddard, F.E. 1885. On the specific characters and structure of certain New Zealand earthworms. Proceedings of the Zoological Society of London, p. 811.
Blackshaw, R.P., and V.I. Stewart. 1992. Artioposthia triangulata (Dendy, 1894), a predatory terrestrial planarian and its potential impact on lumbricid earthworms. Agricultural Zoology Reviews 5, p. 201-219.
Blakemore, R. 2002. Cosmopolitan Earthworms - an Eco-Taxonomic Guide to the Peregrine Species of the World. VermEcology, PO BOX 414 Kippax, ACT 2615, Australia. 506 pp. Edwards C.A., and J.R.Lofty. 1972. Biology of Earthworms. Chapmann and Hall, London. 283 pp.
Johnson, F.H., Shimomura, O., and Y. Haneda. 1965. A note on the large luminescent earthworm Octochaetus multiporus of New Zealand. In: Johnson, F.H., Haneda, Y. (Eds.), Bioluminescence in Progress. Princeton University Press, Princeton, pp. 385-390.
Lee, K.E. 1959. The Earthworm Fauna of New Zealand. New Zealand Department of Scientific and Industrial Research Bulletin No. 130, Wellington, NZ.
Martin NA. 1977. Guide to the lumbricid earthworms of New Zealand Pastures. New Zealand Journal of Experimental Agriculture 5, p. 301-309.
Martin NA. 1982. The interaction between organic matter in soil and the burrowing activity of three species of earthworms (Oligochaeta: Lumbricidae). Pedobiologia 24, p. 185-190.
Smith, W.W. 1887. Notes on New Zealand Earthworms. Transactions of the New Zealand Institute 19, p. 123-139.
Smith, W.W. 1893. Further Notes on New Zealand Earthworms, with Observations on the known Aquatic Species. Transactions of the New Zealand Institute 25, p. 111-146.
Smith, W.W. 1894. Further Notes on New Zealand Earthworms. Transactions of the New Zealand Institute 26, p. 155-175.
Springett, J.A. 1985. Effect of introducing Allolobophora longa Ude on root distribution and some soil properties in New Zealand pastures. In: Fitter, A.H. (Ed.), Ecological Interactions in Soil. Blackwell Scientific, Oxford, UK, p. 399-406.
Springett, J.A. 1987. National assessment of soil forming lumbricids in New Zealand. In: Pagliai, A., Omodeo, P. (Eds.), On Earthworms, p. 497-504.
Springett, J.A. 1992. Distribution of lumbricid earthworms in New Zealand. Soil Biology and Biochemistry 24, p. 1377-1382.
Springett, J.A., and R.A.J. Gray. 1998. Borrowing behaviour of O. multiporus. New Zealand Journal of Ecology 22, p. 95-97.
Springett, J.A., Gray, R.A.J., Barker, D.J., Lambert, M.G., Mackay A.D., and V.J. Thomas. 1998. Population density and distribution the New Zealand indigenous earthworm Octochaetus multiporus (Megascolecidae: Oligochaeta) in hill pastures. New Zealand Journal of Ecology 22, p. 87-93.
Stockdill, S.M.J. 1982. Effects of introduced earthworms on the productivity of New Zealand pastures. Pedobiologia 24, p. 29-35.
Yeates, G.W. 1991. Impact of historical changes in land use on the soil fauna. New Zealand Journal of Ecology 15, p. 99-106.
Yeates, G.W. 1993. Influence of a sabbatical fallow on oligochaetes and nematodes in a hill country pasture. In: Prestige, R.A. (Ed.), Proceedings 6th Australasian Grassland Invertebrate Ecology Conference, p. 142-147.
Oligochaeta Resources on the Web:
Te Ara - The Encyclopedia of New Zealand: WORMS, EARTH
Earthworm Biology Earthworm Information
Encyclopedia: Earthworm
Earthworms
Recognising Australian Earthworms
Earthworms
WormWatch: About earthworms - Ecology, NatureWatch
site.
WormWatch: About earthworms - Taxonomic Key to earthworms, NatureWatch site.
CSIRO Fact sheet: EARTHWORMS
New Zealand Earthworm Association, Inc.
The industrious earthworm, NZ Food & Crop Research
Australian
Faunal Directory:
Checklist for OLIGOCHAETA,
by the Department of Environment and Heritage, checklist of
Australian fauna, with distribution information and bibliography,
with some notes on ecology.
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