Earthworms
Lumbricus, Allolobophora spp., Lumbricidae, OPISTHOPORA

DESCRIPTION

Earthworms or night crawlers are so familiar that little description is needed. Although there are many species which range from 2.5 to 15 cm or more in length when fully grown, all earthworms have the typical earthworm appearance. They are composed of many similar looking segments with a glandular organ, called the clitellum, near the middle of the body.

BIOLOGY

Distribution -- Earthworms occur throughout the United States in almost any moist soil that is loose enough to burrow through and with sufficient organic matter on which to feed. They seek levels in the soil that best suit their needs. As soil dries out they move deeper, but when the soil becomes water-logged, earthworms emerge from the soil to escape drowning. Some species emerge from the soil on moist evenings and feed on the surface near or partly in their burrows.

Damage -- Earthworms do not feed on living plants and generally are considered beneficial for their tilling of the soil. However, earthworm tilling in newly seeded lawns may kill some of the grass seedlings. In established lawns the worms provide a food source for moles whose burrowing damages lawns (see moles). Earthworms that surface leave castings of soil that blemish golf green surfaces. Such castings may harden in lawns during dry weather making the lawn lumpy and crunchy. Walking on such heavily infested lawns is like walking across a field of ping pong balls.

Life History -- The life history of earthworms is peculiar. Not only are they hermaphroditic, they are also homosexual. Although the worms are capable of functioning both as males and as females, only one sex is functional at a time. At the time of mating, both individuals of a pair are males, and they exchange sperm. At a later time the worm becomes a female containing mature eggs. The clitellum then swells into a girdle and secretes a nutritive liquid band. By muscular action this band of nutritive material is pushed slowly forward on the body. As it passes over the female opening, it picks up the eggs and continues to migrate forward to the place where the sperm from the other worm is stored. Sperm is added to the band and the band continues migrating forward until it is sloughed off over the head-end of the worm. The band immediately becomes a closed cocoon which gradually hardens. It is within the cocoon that the sperm finally unite with the eggs. On hatching, the young earthworms feed for a time on the contents of the cocoon before emerging as tiny replicas of their parents. In favorable environments such as those maintained by commercial earthworm growers, the cycle is repeated about once a month.

CONTROL

Few pesticides for control of earthworms or night crawlers are registered and generally available. Soil treatments for control of other soil pests may control some of the worms. For specific chemical controls, consult the state extension service recommendations.