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Common Earthworm

Lumbricus terrestris (aka Night Crawler); they may not be glamorous, but they do serve a very vital function

common earthworm

Description

The night crawler may be up to 10 inches long. The body is divided into 150 ring-like segments. The mouth is at the tapering front end, which is usually slightly darker than the rest of the body; the tail end tends to be more flattened than the head and lighter in color. Its reddish tinge is due to the oxygen-carrying pigment hemoglobin in the blood.

The earthworm's body is made up of segments. On each segment, except the first and last, are four pairs of tiny bristles called setae that help the worm move through the earth. It also has five pairs of "hearts" in the front of its body. The "hearts" help circulate the worm's blood. Waste matter is given off by organs called nephridia, which function like human kidneys. The earthworm has no lungs or gills so it breathes through its thin skin, which is in contact with the air between the particles of soil. When it rains these air spaces fill with water and worms then must come to the surface or drown. If the weather becomes too dry and warm, a worm will die.

earthworm anatomy

Habitat

Earthworms occur in the highest numbers in grassland, where there is plenty of food and no disturbance. Populations decline drastically if the ground is plowed or dug. Moist soils rich in organic matter are the preferred habitat.

Diet

Night crawlers eat a variety of organic matter, including dead leaves and other plant debris, soil micro-organisms (protozoa, nematodes, bacteria, fungi, etc.), and the remains of larger dead animals. Some food is taken in with soil swallowed in burrowing, but vegetation lying on the ground is the most important source.

Reproduction

Earthworms are hermaphroditic, meaning that each individual worm contains both male and female reproductive organs, but a worm must still mate with another in order to reproduce. When two worms mate, they lie alongside one another, and both transfer sperm to the other. Egg-laying begins about a day after mating and may continue for several months afterward. As the eggs are laid they become enclosed in a cocoon and are fertilized by stored sperm. Each cocoon contains several eggs, but in most cases only one or two embryos survive. Young worms emerge after one to five months (the length of time varies according to environmental conditions), and are ready to reproduce after another six to eighteen months.

earthworm reproduction

Movement

Earthworms move along by waves of muscular contraction traveling back along the body. Extra grip is given by short, backwardly-pointing bristles (setae), which can be pushed out as required. There are four pairs of setae on each segment, except the first and last. The setae also serve to anchor the worm in its burrow, which is why it can be extremely difficult to pull a worm out of the ground.

diagram of earthworm musculature and how it helps it move

Benefit to Agriculture

Earthworms move an incredible amount of soil as they burrow and feed. There may be as many as 3 million earthworms per acre of soil, and it has been estimated that 7 to 18 tons of soil can be thrown up by earthworms per acre per year.

Scientific Classification

phylum Annelida
class Oligochaeta
order Haplotaxida
suborder Lumbricina
family Lumbricidae
genus & species Lumbricus terrestris


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PRINT SOURCE
Molly McLaughlin. Earthworms, Dirt, and Rotten Leaves. New York: Avon Books, 1986.

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The Robinson Library >> Science >> Zoology >> Phylum Annelida

This page was last updated on 04/25/2017.