Earthworms

Earthworms are particularly affected by intensive cultivation due to direct impacts during cultivation processes but also because very intensively cultivated systems often don’t have regular inputs of organic materials to keep the worms fed.

There are 27 British species of earthworms; some non-native species have also been introduced accidently. Earthworms can be grouped by their habits, as well as their biology. There are four main earthworm lifestyles:

  • Compost worms like warm moist environments with plenty of fresh organic materials, which they can break down very quickly, as their name suggests commonly there are found in compost bins.
  • Epigeic worms live on the soil surface in leaf litter; they live and feed in the leaf litter. These are commonly found in woodland systems and are rarely found in agricultural soils.
  • Endogeic worms live in the soil and feed on the organic matter they find there. They make horizontal burrows to feed and to move in, which they might re-use. They leave casts within the soil and can be found into the subsoil.
  • Anecic worms make deep permanent vertical burrows. They come to the soil surface in the evening and overnight to gather litter and fresh organic materials and drag them back down their burrows. These worms leave casts on the surface and make middens around the entrance to their burrows.

Earthworms are seasonal in their activity. The shallow-dwellers (endogeic) are active in spring and autumn but generally enter a resting state in summer and winter. When the soil starts to dry out in late spring, the shallow-dwellers move a little deeper (perhaps 30-35 cm deep), curl up in a ball, and secrete a mucus to protect themselves from drying out. They often enter into a hibernation state for the winter. The anecic worms also tend to be more active in spring and autumn, but they may not go into a complete resting state in summer or winter since they can retreat to the bottom of their burrows during extremes of heat or cold.

Earthworm numbers are affected by many different factors – soil type, weather and land management. So just measuring once won’t give a full picture of the numbers or species present – it’ll just be a snapshot.

There is no right number of earthworms

But a series of measurements taken in a number of fields or over a number of years or crop rotations can give an indication of the biological health of your soil. The best time to observe or count earthworm populations is early- to mid-spring or after the soil has wetted up in autumn.

When you are doing a visual assessment of soil structure or digging a soil pit, don’t forget to look out for worms and the signs of their activity (casts and burrows).

Resources

Recommended further reading / online links etc


 [VAC1]Link to Tools page for click to access OPAL guide for earthworms