A few of these creatures are pests but some also provide some biocontrol of nematodes. The earthworms in Ontario are immigrants like most of us. The glaciers that receded over 10,000 years ago, scoured and deposited the parent materials for our soils, leaving little or no life behind. Our earthworms came with the settlers on seeds and plants and as earthen ballast from the ships. Earthworms can number in the thousands per square metre under a pasture or as little as 10 per square metre under an intensive crop rotation.
Earthworms burrow extensively in the soil creating macropores which improve drainage.
The soil passes through the gut of the earthworm and the nutrient rich feces are plastered along the burrow walls. Often you will see plant roots make use of these burrows, due to the ease of rooting, good aeration and abundant nutrients. On the soil surface, dew worms burrows can easily be identified by the pile of castings and crop residues also called middens. Seagulls are often blamed for the loss of earthworms during plowing but studies have shown that the tillage action actually has a greater detrimental effect than the seagulls. The birds are eating injured worms and other soil animals for the most part.