What is an earthworm?

An earthworm is a terrestrial annelid worm belonging to the class Oligochaeta. They can be found in moist soils worldwide and sustain themselves by feeding on decaying plants and organisms, ingesting soil, sand, and tiny pebbles in the process. Earthworms are hermaphroditic, possessing both male and female reproductive organs. During mating, two earthworms exchange sperm, and the eggs are fertilized in a cocoon. Earthworms play a vital role in soil health by aerating the soil, promoting drainage, and enriching it with organic material, which benefits plant growth.

What kind of animal is an annelid?

Annelids are invertebrate animals characterized by their segmented bodies, a body cavity, and movable bristles. They likely evolved in the sea from ancestral flatworms. The phylum Annelida includes more than 9,000 species, divided into three classes: marine worms (Polychaeta), earthworms (Oligochaeta), and leeches (Hirudinea). Earthworms, such as Lumbricus terrestris , are terrestrial worms found in moist soils worldwide. They have ring-like segments and internal organs that repeat in each segment. Earthworms feed on decaying organic matter, ingesting soil as they eat. They are hermaphroditic, and enrich the soil through aeration and decomposition of organic material.

How is an earthworm's body structured?

The body of an earthworm is divided into ring-like segments, up to 150 in some species, with some internal organs repeated in each segment. Between segments 32 and 37 is the clitellum , which creates a cocoon for the earthworm's eggs. The earthworm's body wall consists of an outer layer of circular muscle and an inner layer of longitudinal muscle. Setae , which are bristles embedded in the body wall, may be simple, S-shaped, forked, or hairlike. Except for the first segment, each segment may have two pairs of S-shaped setae or a circle of setae. The coelom, a fluid-filled cavity, lies inside the body between the body wall and the gut and is divided into successive segments in some annelids, including earthworms. The digestive system of an earthworm is a tubular system.

What do earthworms eat and how do they get their food?

Earthworms consume decaying plants and other organisms, incidentally ingesting soil, sand, and tiny pebbles. They possess a straight digestive system; the mouth leads into a muscular pharynx, then to the esophagus, and subsequently to a muscular gizzard. The intestine, which runs most of the worm's length, concludes at the anus. An earthworm can ingest and discard its own weight in food and soil daily. Calciferous glands in some earthworms release calcium by secreting calcium carbonate granules, which transform into calcite crystals in the intestine.

How do earthworms help keep soil healthy?

Earthworms enhance soil health through several activities. They aerate the soil, improving drainage, and pull organic material into their burrows, which boosts the decomposition of organic matter and makes more nutrients available for plants. As earthworms consume decaying plants, they also ingest large amounts of soil, sand, and tiny pebbles, processing and enriching the soil as it passes through their bodies. Their activity of passing soil and organic matter through their bodies helps develop the soil structure, which is critical for plant and other organism support.

How do earthworms move and breathe without lungs or legs?

Earthworms, belonging to the phylum Annelida, move without legs using a coordinated contraction of their circular and longitudinal muscles. Each segment of their body alternately elongates and shortens through peristaltic contractions, creating waves of movement that propel them forward or backward. Setae, bristle-like structures, anchor the worm to the surface during longitudinal muscle contraction, preventing backward slippage. Earthworms lack lungs; instead, they breathe through their skin. Oxygen is absorbed directly through the moist skin into the circulatory system, where it is transported throughout the body. This necessitates a moist environment for the earthworm to facilitate gas exchange.

earthworm

Introduction References & Edit History Quick Facts & Related Topics

Images & Videos

Follow a burrowing earthworm seeking soil's moisture to protect its oxygen-collecting skin

Investigate how muscles in the body wall and small bristles enable earthworms to move through soil

Diagram of an earthworm showing its nervous system, including labeled parts such as the cerebral ganglia, mouth, circumoesophageal connective, subesophageal ganglion, and ventral nerve cord, with an inset of the whole earthworm body.

Illustrations of various invertebrate animals are shown, including a freshwater sponge, sea anemone, sea gooseberry, planarian, whelk, sea urchin, earthworm, centipede, fly, crab spider, and crawfish.

Quick Facts

Also called:: angleworm

Key People:: Charles Darwin

Related Topics:: oligochaete; Lumbricus; night crawler; Oriental earthworm

See all related content

earthworm

annelid

Also known as: angleworm

Written and fact-checked by

Britannica Editors

Last updated

Sep. 19, 2026 •History

Top Questions

What is an earthworm?
An earthworm is a terrestrial annelid worm belonging to the class Oligochaeta. They can be found in moist soils worldwide and sustain themselves by feeding on decaying plants and organisms, ingesting soil, sand, and tiny pebbles in the process.

Earthworms are hermaphroditic, possessing both male and female reproductive organs. During mating, two earthworms exchange sperm, and the eggs are fertilized in a cocoon. Earthworms play a vital role in soil health by aerating the soil, promoting drainage, and enriching it with organic material, which benefits plant growth.
4 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What kind of animal is an annelid?
Annelids are invertebrate animals characterized by their segmented bodies, a body cavity, and movable bristles. They likely evolved in the sea from ancestral flatworms. The phylum Annelida includes more than 9,000 species, divided into three classes: marine worms (Polychaeta), earthworms (Oligochaeta), and leeches (Hirudinea). Earthworms, such as Lumbricus terrestris, are terrestrial worms found in moist soils worldwide. They have ring-like segments and internal organs that repeat in each segment. Earthworms feed on decaying organic matter, ingesting soil as they eat. They are hermaphroditic, and enrich the soil through aeration and decomposition of organic material.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How is an earthworm's body structured?
The body of an earthworm is divided into ring-like segments, up to 150 in some species, with some internal organs repeated in each segment. Between segments 32 and 37 is the clitellum, which creates a cocoon for the earthworm's eggs.

The earthworm's body wall consists of an outer layer of circular muscle and an inner layer of longitudinal muscle. Setae, which are bristles embedded in the body wall, may be simple, S-shaped, forked, or hairlike. Except for the first segment, each segment may have two pairs of S-shaped setae or a circle of setae.

The coelom, a fluid-filled cavity, lies inside the body between the body wall and the gut and is divided into successive segments in some annelids, including earthworms. The digestive system of an earthworm is a tubular system.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What do earthworms eat and how do they get their food?
Earthworms consume decaying plants and other organisms, incidentally ingesting soil, sand, and tiny pebbles. They possess a straight digestive system; the mouth leads into a muscular pharynx, then to the esophagus, and subsequently to a muscular gizzard. The intestine, which runs most of the worm's length, concludes at the anus. An earthworm can ingest and discard its own weight in food and soil daily. Calciferous glands in some earthworms release calcium by secreting calcium carbonate granules, which transform into calcite crystals in the intestine.
2 Britannica Sources
1. earthworm
2. annelid: Digestive system
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How do earthworms help keep soil healthy?
Earthworms enhance soil health through several activities. They aerate the soil, improving drainage, and pull organic material into their burrows, which boosts the decomposition of organic matter and makes more nutrients available for plants. As earthworms consume decaying plants, they also ingest large amounts of soil, sand, and tiny pebbles, processing and enriching the soil as it passes through their bodies. Their activity of passing soil and organic matter through their bodies helps develop the soil structure, which is critical for plant and other organism support.
2 Britannica Sources
1. soil organism
2. earthworm
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How do earthworms move and breathe without lungs or legs?
Earthworms, belonging to the phylum Annelida, move without legs using a coordinated contraction of their circular and longitudinal muscles. Each segment of their body alternately elongates and shortens through peristaltic contractions, creating waves of movement that propel them forward or backward. Setae, bristle-like structures, anchor the worm to the surface during longitudinal muscle contraction, preventing backward slippage.

Earthworms lack lungs; instead, they breathe through their skin. Oxygen is absorbed directly through the moist skin into the circulatory system, where it is transported throughout the body. This necessitates a moist environment for the earthworm to facilitate gas exchange.
4 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

earthworm, any one of more than 1,800 species of terrestrial worms of the class Oligochaeta (phylum Annelida)—in particular, members of the genus Lumbricus. Seventeen native species and 13 introduced species (from Europe) occur in the eastern United States, L. terrestris being the most common. Earthworms occur in virtually all soils of the world in which the moisture and organic content are sufficient to sustain them. One of the most detailed studies of earthworm activities was conducted by English naturalist Charles Darwin.

Members of one Australian species can grow as long as 3.3 metres (about 11 feet). L. terrestris grows to about 25 centimetres (10 inches). This species is reddish brown, but some earthworms (e.g., Allolobophora chlorotica, native to Great Britain) are green. The reddish tinge of L. terrestris results from the presence of the pigment hemoglobin in its blood.

The earthworm body is divided into ringlike segments (as many as 150 in L. terrestris). Some internal organs, including the excretory organs, are duplicated in each segment. Between segments 32 and 37 is the clitellum, a slightly bulged, discoloured organ that produces a cocoon for enclosing the earthworm’s eggs. The body is tapered at both ends, with the tail end the blunter of the two. Earthworms cannot see or hear, but they are sensitive to both light and vibrations.

Britannica Quiz

Match the Baby Animal to Its Mama Quiz

Their food consists of decaying plants and other organisms; as they eat, however, earthworms also ingest large amounts of soil, sand, and tiny pebbles. It has been estimated that an earthworm ingests and discards its own weight in food and soil every day.

Earthworms are hermaphroditic; i.e., functional reproductive organs of both sexes occur in the same individual. The eggs of one individual, however, are fertilized by the sperm of another individual. During mating two earthworms are bound together by a sticky mucus while each transfers sperm to the other. The worms separate and form cocoons; the cocoon moves forward, picking up eggs at the 14th segment; at the 9th and 10th segments it picks up the sperm deposited by the other earthworm. The cocoon slides over the head, and fertilization takes place. Within 24 hours after the worms mate, the cocoon is deposited in the soil.

Miniature earthworms usually emerge from the cocoon after two to four weeks. They become sexually mature in 60 to 90 days and attain full growth in about one year.

Earthworms usually remain near the soil surface, but they are known to tunnel as deep as 2 m during periods of dryness or in winter. One Asian species is known to climb trees to escape drowning after heavy rainfall.

Explore Britannica Premium!

The trusted destination for professionals, college students, and lifelong learners.

Earthworms provide food for a large variety of birds and other animals. Indirectly they provide food for humans by assisting plant growth. Earthworms aerate the soil, promote drainage, and draw organic material into their burrow. This last service accelerates the decomposition of organic matter and produces more nutritive materials for growing plants. Earthworms also serve as fish bait; hence, the name angleworm.

This article was most recently revised and updated by Amy Tikkanen.

earthworm

Thank you for signing up!