There are over 180 species of earthworms in the United States and Canada, but only 60 of these are native to the area. Settlers brought many of the species to improve the soil, although earthworms are not always beneficial to plants.
While there are more than 6,000 species of earthworms found around the world, the three species most common in the United States are the night crawler, anglerworm and rain worm. Night crawlers are an invasive species that leave the ground at night, while rain worms exit to crawl on sidewalks after a storm. Anglerworms are popular for fishing.
In the United States, earthworms range in size from 1/2 inch to 14 inches in length. However, in the tropics, some species of earthworms reach almost 10 feet in length. One earthworm found in South Africa, was 22 feet long. The normal lifespan of an earthworm is four to eight years, but some of the larger species live almost 50 years.
Earthworms eat soil, leaves and plant material. In the garden, worm castings are beneficial to plants. However, in the northern forest that grew after glaciers killed all the earthworms, they are harmful to trees. These forests need the decaying leaves and organic material, called duff, to survive. As earthworms eat the duff, invasive species take over the forest and the population of insects and salamanders that were dependant on duff for survival decreases.