Nobody knows the total number of worm species but it’s thought to be 7000 species, only about 150 species are widely distributed around the world. These are the peregrine or cosmopolitan earthworms.
What do Earthworms do?
Earthworms are a familiar sight to farmers and are useful in maintaining healthy and organic-rich soils;
Earthworms can be active throughout the year but are quiescent during cold or hot and dry weather. They occur in most soils, but are scarce in soils that are extremely acidic or prone to water-logging.
Earthworms eat decaying plant material and do not damage growing plants. They are important to soil structure and fertility.
Some earthworms emerge at night to feed on dead plant material on the surface, and will pull fallen leaves and other plant debris into their tunnels
Some species such as Allolobophora nocturna, A. longa and Lumbricus terrestris live in permanent burrows and it is mainly these species that produce worm casts on the surface.