Earthworm facts for kids
Quick facts for kids Earthworm |
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| An unidentified earthworm species with a well-developed clitellum | |
Scientific classification  |
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| Kingdom: | Animalia |
| Phylum: | Annelida |
| Class: | Clitellata |
| Order: | Opisthopora |
| Suborder: | Lumbricina |
An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They occur worldwide where soil, water, and temperature allow.
Earthworms activity aerate and mixe the soil, making it more fertile and rich in nutrients. An abundance of earthworms is generally considered beneficial by farmers and gardeners. As long ago as 1881 Charles Darwin wrote: "It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organized creatures."
Contents
Description
The average earthworm is a reddish brown color, with a pointed posterior and anterior end. There are no eyes or other discerning facial features, only a simply opening for a mouth. Earthworms have long, segmented bodies, covered in microscopic setae, or bristles, which help to anchor and pull the worm via longitudinal muscle contractions. Earthworms have no lungs, and absorb oxygen directly through their skin. In order to do this, they must stay moist, and do so by lubricating their skin with glands along their bodies.
Earthworms are invertebrates, lacking a skeleton. To support and shape the body, they are filled with coelomic fluid. Earthworms sometimes appear to have a "belt" or "saddle" around their bodies; this is a clitelum, a structure containing maturing eggs.
Size
Their sizes vary: they can be between two centimeters and about three meters in length. The biggest known earthworm is the giant Gippsland earthworm, found in Australia. It is usually about 80cm in length, but can grow to about 2 meters.
The most common earthworm (in Europe, and most other temperate climate regions) grows to a size of about 20-25 cm when extended.
Habitat
Earthworms are commonly found in soil. They can be found everywhere, except in polar or dry climates.
Earthworms typically live in damp (but not wet), loose soil. They can also be found in loose leaf litter, and after it rains they can be found on the surface as they are forced out of the water-logged soil. Many gardeners welcome earthworms, as they aerate and enrich the soil with their droppings. They are quite happy in compost, gorging themselves on decaying vegetable matter. An earthworm's burrow can be seen by the pile of dark, sand-like droppings, or casts, surrounding the entrance.
Diet
The typical earthworm diet is decaying matter, leaf litter, microbial fungi, and other microscopic organisms. Earthworms are important to the environment, breaking down organic matter and passing it through their gut as newly enriched soil. An earthworm has no teeth, so it swallows grit to help grind food in its multi-chambered gut. As an earthworm burrows and feeds, it aerates the soil and adds nutrients from deeper soil layers to upper layers, making easier new plant growth in the process. For this reason, they are valued by farmers and gardeners worldwide.
Reproduction
Earthworms are hermaphrodites, meaning they each contain male and female gametes. During mating, both worms exchange sperm and have eggs fertilized. The belt-like swollen area on the earthworm’s body, commonly called the "saddle" or "belt", is called a clitelum. It secretes a slimy substance that forms capsules which protect the eggs (sperm cells and eggs merge inside the capsule and form embryos). Inside, 1-20 eggs mature, taking between 60 and 90 days to hatch, depending on environmental factors such as humidity and temperature. An earthworm takes up to a year to fully mature, and in the wild they can live from 4 to 8 years.
Life and physiology
At birth, earthworms emerge small but fully formed. They only lack sex structures which develop in about 60 to 90 days. They become fully grown in about one year. Scientists predict that the average lifespan under field conditions is four to eight years, while most garden varieties live only one to two years.
Locomotion
Earthworms travel underground thanks to muscular contractions which alternately shorten and lengthen the body. As they burrow, their body secrets lubricating mucus. As a result of their movement through their lubricated tunnels, worms can make gurgling noises underground when disturbed. Earthworms move through soil by expanding crevices with force; when forces are measured according to body weight, hatchlings can push 500 times their own body weight whereas large adults can push only 10 times their own body weight.
Ecology
Earthworms are classified into three main ecophysiological categories:
- (1) leaf litter- or compost-dwelling worms that are nonburrowing, live at the soil-litter interface and eat decomposing organic matter;
- (2) topsoil- or subsoil-dwelling worms that feed (on soil), burrow and cast within the soil, creating horizontal burrows in upper 10–30 cm of soil; and
- (3) worms that construct permanent deep vertical burrows which they use to get plant material for food, such as leaves, from the surface.
Predators
Earthworms are preyed upon by many species of birds (e.g. robins, starlings, thrushes, gulls, crows), snakes, wood turtles, mammals (e.g. bears, boars, foxes, hedgehogs, pigs, moles) and invertebrates (e.g. ants, flatworms, ground beetles and other beetles, snails, spiders, and slugs).
Earthworms have many internal parasites; they can be found in the worms' blood, seminal vesicles, coelom, or intestine, or in their cocoons.
Environmental impacts
The major benefits of earthworm activities to soil fertility for agriculture can be summarized as:
- Biological: In many soils, earthworms play a major role in the conversion of large pieces of organic matter into rich humus, thus improving soil fertility.
- Chemical: In addition to dead organic matter, the earthworm also ingests any other soil particles that are small enough, grinding everything into a fine paste which is then digested in the intestine. When the worm excretes this in the form of casts, minerals and plant nutrients are changed to an accessible form for plants to use.
- Physical: By creating burrows and channels in the soil, earthworms maintain soil structure, aeration, and drainage.
Economic impact
Various species of worms are used in vermiculture, the practice of feeding organic waste to earthworms to decompose food waste. These are usually Eisenia fetida (or its close relative Eisenia andrei) or the brandling worm, commonly known as the tiger worm or red wiggler. They are distinct from soil-dwelling earthworms. In the tropics, the African nightcrawler Eudrilus eugeniae and the Indian blue Perionyx excavatus are used.
Earthworms are sold all over the world. According to Doug Collicutt, "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 an excellent source of protein for fish, fowl and pigs. They were also used traditionally for human consumption. Noke is a culinary term used by the Māori of New Zealand, and refers to earthworms which are considered delicacies for their chiefs.
Interesting facts about earthworms
- An earthworm breathes through its skin.
- Earthworms are hermaphrodites: each carries male and female reproductive organs.
- They lack a true skeleton, but they maintain their structure with fluid-filled coelom chambers that function as a hydrostatic skeleton.
- There are 5,500 known species of worms.
- An earthworm's digestive system is as long as its body.
- Most earthworms can regrow lost segments, assuming the worm has not had too much damage. This capability varies by species.
- The longest worm on confirmed records is Amynthas mekongianus that extends up to 3 m (10 ft) in the mud along the banks of the 4,350 km (2,703 mi) Mekong River in Southeast Asia.
- Salt on human skin is toxic to earthworms because it dehydrates them. That is why they wriggle, when people touch them with bare hands.
- An earthworm has a brain, nerves, and heart.
- From a total of around 7,000 species, only about 150 species are widely distributed around the world. These are the peregrine or cosmopolitan earthworms.
- Of the 182 taxa of earthworms found in the United States and Canada, 60 (33%) are introduced species.
- Nitrogenous fertilizers create acidic conditions, which are fatal to the worms.
- The population size of the earthworm indicates the quality of the soil, as healthy soil would contain a larger number of earthworms.
- Investigations in the United States show that fresh earthworm casts are five times richer in available nitrogen, seven times richer in available phosphates, and 11 times richer in available potassium than the surrounding upper 6 inches (150 mm) of soil.
- Each person alive today has support of 7 million earthworms.
Images for kids
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Nervous system of the anterior end of an earthworm
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A profile SEM image of Lumbricus terrestris setae, small bristle-like projections that facilitate movement by anchoring the earthworm in the soil.
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An earthworm cocoon from L. rubellus
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Devil's coach horse beetle preying on Lumbricus sp.
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Faeces in the form of casts
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Earthworms being raised at La Chonita Hacienda in Mexico
See also
