Most widespread soil engineer

There are more than 6,000 named species of earthworms (order Opisthopora) found everywhere except very cold and very arid regions on all continents bar Antarctica. They are often locally abundant and diverse. All earthworms are well-recognized for their soil engineering. Burrowing aerates and mixes soil, increasing water infiltration and drainage, and rates of organic matter breakdown. Many species drag litter into their burrows increasing the organic matter content. It is likely that, globally, earthworms have more influence on soils than termites (which are geographically less widespread) and ants (which perform less soil bioturbation in cooler regions), although all three kinds of macro-invertebrates combined engineer more soil on the planet than any other group of animals.

In his last book, The Formation of Vegetable Mould Through the Action of Worms (1881), Charles Darwin said: “It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organised creatures.”

Some regions of North America lost earthworms during glaciation (the last Ice Age). Exotic earthworm species that have been introduced inadvertently via plant pots or accidentally released from worm farms raising bait for fishing are now causing disruption.