The drilosphere is the part of the soil influenced by earthworm secretions, burrowing and castings.
[3] The average thickness of the drilosphere (lining of an earthworm burrow) is 2 mm,[4] but it can be much wider (about 8 mm) around the burrows of litter-feeding earthworms.
[5] Through the drilosphere, earthworms influence soil microbial communities, with effects on microbial processes related to soil organic matter and nutrient dynamics.
[7] The drilosphere is generally richer in nitrogen, phosphorus, and humified organic material than the surrounding soil.
This is probably because earthworms preferentially ingest plant residue such as leaf and root litter, or occasionally fungi.