The soil is not a solid indivisible block but consists of innumerable aggregations of matter, organic and inorganic interspersed with an equally innumerable number of small pores. Life in the soil is lived on a micro scale, and these small pores are large habitable spaces to the organisms that use them. Living in the soil is a bit like living in an endless series of interlinked caves, a huge 3D matrix of high class accommodation, with plenty of food, and very stable environmental conditions. Like a tropical Rainforest the temperature in the soil is fairly constant, much more so than the air above, a couple of centimetres down the soil rarely if ever freezes, even when it is twenty below above. The humidity, which is very important to many organisms, is high and much more constant than on the surface.

The soil is not only a full time home to millions of these small animals but is also a temporary escape from the elements for many others, huge numbers of beetles, flies, and moths lay there eggs in the soil and have there larvae live there, as well as this many Bees and Wasps make there nests in it. Amongst the vertebrates many, particularly Shrews, Voles, and Moles live and feed in it, Weasels and Badgers live in it and feed on the other animals which use it, Rabbits live in it while many birds also make a living feeding on the creatures that live there. All these burrowing mammals are important in shifting and mixing the soil, however though often more visible there efforts are relatively unimportant in comparison with the work done by worms.

This is particularly true of temperate soils, in some tropical soils millipedes, termites and ants are often the dominant soil movers. In some places in Britain there are 1 ton earthworms per acre which move well over 10 tons of soil per year.

Earthworms were described by Aristotle as 'the intestines of the earth'. Numerous soil scientists have been equally fascinated by the amount of work done by them, Charles Darwin said of them "It may be doubted whether there many other animals which have played so important a part in the history of the world as these lowly organised creatures". Earthworms are miniature topsoil factories, earthworms make soil, all other living things eventually pass through an earthworm on the way to becoming soil, and nearly every atom in your body has been in an earthworms stomach before it was part of you, (salt is an exception). Earthworm castings are rich in all the minerals necessary for plant growth, in a water soluble form so that they are immediately available for plant use. All the soil you have ever seen has passed through the stomachs of numerous earthworms to become what it is. Earth worms are amazingly strong, and can easily shift stones 60 times there own weight.
The best way to deal with those unwanted earthworm casts on your lawn is to collect them and use them as potting compost, no manufacturer can make anything better suited to the growth of seedlings.

Information provided by: http://www.earthlife.net