Where earthworms are active, burrows form an inter-connecting network of vertical and horizontal tunnels. They are very stable and may last many years. It is the burrows that aid the penetration of water and roots into the soil. As temperatures rise and the soil becomes dry, earthworms burrow to a depth of 25 to 40 cm and rest. They tolerate dry summers, but long droughts will kill them.
Some species can withstand the loss of much body fluid during dry conditions.
They regain weight when moisture is available again. Casts Casts are aggregates of soil, and are often more stable than surrounding soil. Some earthworms, but not all, deposit casts on the surface. In the United Kingdom, where earthworm numbers range from 1.2 to 21.5 million per hectare, up to 25 tonnes of casts per hectare can be produced each year. Much less would be produced in our wheatbelt since we have smaller earthworm populations, less organic matter and a summer drought.