Worms provide a tremendous boon to gardens, as they feed on litter and debris and convert it to a mucus-rich excrement loaded with nutrients and minerals that forms a foundation of quality soil, according to Adrian Card of the Colorado State University Extension. You can attract different types of earthworms and encourage their activity by watering your garden without oversaturating it and providing food sources including grass clippings, organic mulch and "green manure," such as cover crops that get plowed under in the spring.
The nightcrawler or dew worm, a deep burrowing or anecic earthworm, can be brown, red or sometimes greenish and grows up to 12 inches long. The genera Lumbricus belongs to the earthworm family of Lumbricidae, which also includes the genera of Eisenia, Dendrobaena and Allolobophora.
The redworm, a litter-dwelling or epigeic earthworm, grows up to 3 inches long and has from 95 to 120 segments and no stripes.
This grayish-blue worm, about 3 to 4 inches long, is the common earthworm, also called the field earthworm.
Red wigglers prefer to live their lives on farms with manure to feed on but may be introduced to gardens by birds, the use of farm manure, or via compost from an indoor worm bin, where they account for most of the worms used in home vermiculture. Red wigglers are reddish brown and grow about to be about 3 inches long. Their bodies have alternating, subtle bands of yellow and maroon. This hardy worm tolerates cold winters well and is found in Alaska.
The European nightcrawler resembles a larger version of the red wiggler, growing 3 to 8 inches long; these also are known as super reds. Like red wigglers, these worms can adapt exceptionally well to life in an indoor or outdoor compost bin.
The warmth-seeking blue worm lives in the southern and Gulf Coast states, as well as in Hawaii and Puerto Rico. These worms grow to between 1 and 3 inches and feature dark red-brown hind parts and a purple head.
This earthworm grows to be about 4 to 6 inches long and can be pink or brown. Like the blue worm, it prefers warm weather and grows well in the southeastern United States.
African nightcrawlers, growing to about 10 inches long, need temperatures above 50 degrees to survive, so it is most likely to be found in tropical or subtropical gardens. These are the largest of the worms suitable for composting and prefer a toasty 80 degrees to flourish, according to MonsterWorms.