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Oligochaeta

What do they look like?

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. They have no skeleton, but do have lots of muscles. Earthworms don't have much coloration, so they usually look white, gray, pink, or reddish brown. Some earthworms have red blood, and you can see it through their skin. Their skin produces slimy mucus that helps them slide through the soil. Like most animals they have a front and back end, and their mouth and tiny brain are at the front. They don't have eyes or a nose, but can detect light and vibrations, and have senses of touch and taste. Some earthworm species are very small, less than 1mm long, but some are the biggest worms in the soil. In North America the biggest are almost 30 cm long, and Australia there are some that grow to over 2 meters long!

Where do they live?

Earthworms and their aquatic relatives are found all over the world. There are several thousand species! Most live in muck and mud around freshwater, but some live under the sea, and many live in the soil on land. This account is mainly about the earthwoms that live on land. There are at least 21 species of earthworms in Michigan. Some of the biggest and most common species of earthworms in North America were accidentally brought there by colonists from Europe.

What kind of habitat do they need?

Earthworms and their relatives live anywhere there is moist soil and dead plant material. Earthworms are most abundant in rainy forest areas, but can be found in many habitats on land and in freshwater. All earthworm species need moist soil conditions to survive.

Most earthworms species live in the top meter or so of soil, and spend much of their time just below the surface where there is plenty of decomposing plant material. Some species emerge onto the surface at night when it is damp enough. They go deeper to avoid droughts or winter freezes. Some species never come to the surface, and spend their whole lives meters below the surface. Worm tunnels have been found to go at least 5 meters (16.5 ft.) below the surface!

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams
  • temporary pools

How do they grow?

Earthworms lay their eggs in cocoons that they make in the soil. The little worms that hatch out look like tiny versions of the adults, and they don't change much as they grow, they just get bigger. Species that live in very cold or hot and dry climates may go dormant when it is too cold or dry. Some only survive the winter or summer as eggs.

How long do they live?

Some earthworm species can live up 8 years, but it is very rare for them to survive that long. Most are eaten or killed in some other way before they live for one year.

How do they behave?

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.

How do they communicate with each other?

Earthworms only communicate with each other by touch and taste, but they can feel vibrations, and often avoid predators by sensing their footsteps. They can also sense light and moisture in the air.

What do they eat?

Earthworms eat dead and decaying plant material, mostly leaves, but also tiny roots and other bits. Some species live down deep in the soil and eat dead roots.

What eats them and how do they avoid being eaten?

Earthworms' main defense is hiding in their burrows in the soil. They will quickly crawl down into the ground if they detect a predator. Some can secrete bad-tasting chemicals. Some can also grow a new tail.

What roles do they have in the ecosystem?

Earthworms are very important to the soil. They carry organic material down into the lower levels, they break down dead plant material, and their burrows help air and water get deeper into the soil.

Do they cause problems?

Earthworms sometimes damage seedlings of valuable plants, and by moving around in the soil may spread plant diseases. Some earthworms also carry animal parasites that grow in their predators.

How do they interact with us?

Earthworms are usually very beneficial. Their tunneling and feeding helps to enrich soil, promoting better plant growth.

Are they endangered?

Earthworms as a group are very common and abundant, and are not in need of special protection. We don't know very much about most species though, so some rare species could be in danger.

  • IUCN Red List [Link]
    Not Evaluated

Some more information...

It's not true that if you cut a worm into bits the parts will grow. Sometimes they can grow a new tail, but that's it. The worms that come out during rainstorms are looking for new places to live, and often get trapped in puddles. They can live in water (they get oxygen through their skin), but they will die from too much sunlight, or if there is salt or other toxic chemicals in the puddles.

Some people keep boxes of worms and dirt. They feed the worms kitchen scraps, and then put the worms and dirt in their gardens.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends.

biodegradation

helps break down and decompose dead plants and/or animals

bog

a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

chaparral

mid-altitude coastal areas with mild, rainy winters and long, dry summers. Dominant plant types are dense, evergreen shrubs.

chemical

uses smells or other chemicals to communicate

cosmopolitan

having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.

detritivore

an animal that mainly eats decomposed plants and/or animals

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

freshwater

mainly lives in water that is not salty.

heterothermic

animals that have little or no ability to regulate their body temperature, body temperatures fluctuate with the temperature of their environment, often referred to as 'cold-blooded'.

internal fertilization

fertilization takes place within the female's body

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

parthenogenic

development takes place in an unfertilized egg

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Climbing plants are also abundant. There is plenty of moisture and rain, but may be somewhat seasonal.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

soil aeration

digs and breaks up soil so air and water can get in

solitary

lives alone

suburban

living in residential areas on the outskirts of large cities or towns.

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

taiga

this biome is characterized by large expanses of coniferous forest, there is an extended cold season and heavy snowfall.

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland
savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland
urban

living in cities and large towns, landscapes dominated by human structures and activity.

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

year-round breeding

breeding takes place throughout the year

 
University of Michigan Museum of ZoologyNational Science Foundation

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BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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