How do earthworms locate humus enriched soil when soil is infertile and humus is added?

Through their sensitivity detectors and by way of their passage forming movements earthworms [of the Lumbricina suborder] locate the humus enriched areas of otherwise infertile soil. Humus refers to the dark brown, fresh smelling, nutrient rich organic matter in soil. Its formation occurs naturally with the breakdown of dead and decaying animal and plant matter within soil. So earthworms have chemically related senses of where humus is. They can pick humus out from a crowd of competing living and non living dwellers of the underground. Additionally, they're sources of humus themselves through their waste products, which are often nitrogen rich.