There are three types of earthworm: those that live on the surface, others that feed and dwell in the soil, while a third group makes deep burrows and comes to the surface to feed on dead leaves.
All are vital to the soil health, providing nutrients and drainage, so it is concerning when they are scarce or absent on farmland.
Particularly at risk are epigeic earthworms (surface dwellers), which have vanished in some fields in Britain due to intensive farming practices, mostly excessive tillage and overuse of chemicals.
Their disappearance means poor soil fertility, lower crop yields and loss of carbon from the soil, a factor exacerbating climate change. It also partly explains the crash in the song thrush population, which relies on this type of worm to feed its young in the spring.
Researchers asked farmers to dig pits in their fields and count the number of worms of each type they found. The average field had nine per spadeful, but the best fields with healthy soil had three times that number. More than half the farmers were so alarmed by the results they pledged to change their practices.
