This is much better than a dry or granular fast-acting chemical fertilizer which has no humus, leaches away and may repel the worms. Earthworms usually dwell in the top few centimetres of the soil, but some species will go down nearly 2m. They need moisture to breath, and burrow deeper if the soil dries out or freezes. However, they will drown in waterlogged soil so the recent wet conditions has not been helpful. They come to the soil surface at night when temperatures are lower and humidity higher.
Most soil types are suitable except very acidic, and coarse sand.
They can reproduce when 3 - 6 weeks old, making a cocoon in the soil from which live worms emerge. The common view that cutting a worm in half makes two is not true, they can regenerate body parts in some cases, but usually both parts die. Unfortunately the worm population of Northern Ireland and Co Down in particular, is under great threat at present from the New Zealand Flatworm . This interloper feeds exclusively on earthworms and can reduce the numbers to below detectable levels in the right conditions. To increase the worm population, adding organic matter provides food and adding lime to acidic soil will help.