Earthworm
Scientific name
- Scientific name
- Lumbricina
How to say it in other languages
- Chinese
- 蚯蚓
- Dutch
- Regenwormen
- Hindi
- केंचुआ
- Japanese
- ミミズ
- Portuguese
- Minhoca
- Russian
- Дождевые черви
Facts from Wikipedia’s “Earthworm” page and Wikispecies (CC BY-SA 4.0).
An earthworm is an invertebrate animal with a long, stretchy body and no legs. It is a type of annelid worm.
There are over 5,500 known species of earthworms in 21 families. They are found everywhere, except in polar or dry climates. 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 80 cm in length, but can grow to about 3 meters.
The most common earthworm (in Europe, and most other temperate climate regions) grows to a size of about 20–25 cm when extended.
Most earthworms can regrow lost segments, assuming the worm has not had too much damage. This capability varies by species.
Long ago, all animals looking like worms were lumped together by John Ray and by Linnaeus in their classifications. Later, biologists found that some were in quite different groups. Roundworms and flatworms are different phyla. Inchworms are a type of caterpillar, and the slow-worm is a legless lizard.
Physical characteristics
The average earthworm is a reddish brown or reddish pink 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.
Earthworm habitats
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 also found in compost, feeding on decaying vegetable matter. An earthworm’s burrow can be seen by the pile of dark, sand-like droppings, or casts, surrounding the entrance.
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.
Diet
The typical earthworm diet is decaying matter, humus, 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.
Written for younger readers
Earthworm, in simpler words
This version comes from Wikijunior, a set of books written for children aged 8 to 11. It is shorter and uses plainer language than the article above.
From Wikijunior: Bugs
Earthworms are smooth-skinned worms, with a body made of many small segments. If you look at the body you can see lines that mark the segments. Each segment has stiff little hairs that help the worm move, sometimes the hairs are hard to see.
The habitat of an earthworm is underground, within the soil. This can take on very different qualities depending on the worm’s location; living underground in a tropical rainforest, for example, leads to much more food but also more risks from predators. An earthworm who lives in poorer soil in temperate regions, by contrast, may have to eat more but has less of a chance of being eaten by predators, like birds, mice, and insects. These worms live underground their entire lives except for during heavy rainfall. Worms cannot survive very wet soil and must rise to the surface to breath when there is excessive rain. Only a few species of worm actually go deeper into the soil in very wet conditions.
Earthworms eat soil. Their nutrition comes from things in soil, such as decaying roots and leaves. Animal manures are an important food source for earthworms. They eat living organisms such as nematodes, protozoans, rotifers, bacteria, fungi in soil.
What earthworms can do is burrow. They have small bristles, known as setae, which are both sensing devices that can identify any soil vibrations and digging aids. The setae stick to dirt and the worm then contracts its body to force itself through soil. The worm also secretes a mucus that helps it slide through dirt more quickly. In fact, to escape the cold of winter or an eager predator, the earthworm can burrow dozens of feet below the surface. Earthworms also are aware of when it’s safest to come out of hiding: at night. The only other time you’re likely to see earthworms is after a rain. This is not necessarily because of what you may have heard, that the worm is trying to avoid drowning. In fact, an earthworm gets its oxygen through its skin, and can survive several weeks if it is submerged. The more likely reason is that the rain keeps the worm from becoming too dry, as it normally would in sunshine, and allows it a chance to find a mate. The earthworm might also be coming to the surface to move more quickly to colonize new ground or to forage for food during weather when predators are less likely to be out.
In earthworms, development of adult is direct. Bugs that have larval stage during development show metamorphosis. Metamorphosis includes larva and pupa stage during development of egg into adult. Earthworms do not show larval and pupa stage during their development
During the day earthworms mostly stay in their burrows underground. At night they come up near or on to the surface to feed. If the air it is too cold or too dry, they stay down in the soil. Some species also come on to the surface during the day if it is raining.
Earthworms are good for plants and good for people because we eat plants. Earthworms are good for all plants and animals because they keep the soil healthy. They harmless to us on our skin but do not like to crawl on us because our skin is too warm for them.
Where this page comes from
The article above is adapted from “Earthworm” on Simple English Wikipedia, by its contributors. We removed reference markers, navigation boxes and tables, expanded measurement templates into readable numbers, and kept the prose otherwise intact. The simpler version is adapted from Wikijunior on Wikibooks.
Both sources are published under CC BY-SA 4.0, so this page is published under the same licence. You may share and adapt it, including commercially, as long as you credit the original and keep the same licence.
Worksheets, answer keys and printable layouts elsewhere on K5Print are our own work and are not covered by this licence.