Earthworms are sensitive to any kind of disturbance of the soil. They will be especially affected by mechanized agriculture and by man-made chemicals. Rainfall will affect earthworms in a different way, when they will often become easy prey for predators after being drawn to the surface. When there is no soil disturbance and not overly moist conditions, then this combination will help to create a suitable area for a healthy and sizable population of earthworms.
Extreme heat will affect earthworms, and as a consequence the soil will not be broken down. When the soil is too hard, earthworms will have difficulty in creating burrows and often struggle to find the organic matter they need to survive. Earthworms will also be caused distress by flooded soil. When their burrows are flooded, earthworms will strive to get away from the affected area. A flooded area of soil will also mean that it will struggle to recover if there are no earthworms left to aerate it.
Lime and loam will create a suitable environment for earthworms, though the amount of lime in the soil should be carefully managed and other nutrients in the soil should not be adversely affected. Soil that is silty, or soil which just contains some clay, will also be beneficial to the earthworm. Calcium and phosphorus in the soil are important factors when keeping the population of earthworms at a high level. Earthworms will not do so well in sandy soil.
Soil that has a plentiful supply of organic matter will be beneficial to earthworms. Organic matter that is really fine will make it easier for a worm to digest its food. Moist soil helps the spread of fungi, that will provide the earthworms with food. A moist soil also makes it easier for earthworms to penetrate the top soil, whereby the earthworm can pull down and eat leaves lying on grass. Bacteria is also an important part of a worm's diet. The worm, in turn, encourages the growth of fungi and bacteria by developing areas in the soil for both to flourish.