Over 2,500 species of earthworms exist. Worms are unusual in that a single worm has both sexes, separated from one another by a ring. Solitary earthmoving worms tunnel through the soil, mixing, decompacting, and aerating soil, enabling nutrients to move from the surface to plant roots. The best worms for composting--Eisenia fetida, Lumbricus rubellus, Eisenia hortensis, and Esenia andreii--live in masses and work on the surface.
Eisenia fetida, also called red wigglers, are about 1 1/2 to 2 1/2 inches long. E. fetida produce about two to five cocoons each week. Each cocoon will hatch two or three worms in about a month and a half. Red wigglers live from 2-5 years.
About two pounds of E. fetida will consume about one pound of scraps each day. E. fetida is the worm usually sold commercially. One pound of E. fetida is good for a compost bin 2 feet by 2 feet. Two pounds of them are good for a bin that is 2 feet by 3 feet.
L. rubellus, which grows to 4 inches long as an adult, is also called an angle worm, leaf worm, garden worms, drift worm, or red March worm. It is longer than E. fetida. L. rubellus will survive at 38 to 40 degrees Fahrenheit, making it a better cold weather worm than Eisenia fetida.
E. hortensis, a large, robust worm reclassified from its former genus name, Dendrobaena veneta, is called the European night crawler or Belgian night crawler. It is finding supporters as a composting worm, especially in commercial systems. E. Horensis is larger than E. fetida; it prefers cooler temperatures and likes a moist environment. It grows far more slowly than E. fetida, often requiring a year and a half to get established in compost.
To a layperson, E. andrei is identical to E. fetida, although it is a deeper color red. It is sometimes called the tiger worm because its segments are divided by a yellow band. E. andrei behaves and performs nearly identically to E. fedita; it is often found in composting bins along with E. fetida without anyone knowing the difference, although some claim that it exudes an unpleasant odor.