Earthworms Underground describes earthworm structures and behaviors with a focus on adaptations that enable earthworms to survive underground. These adaptations include being able to breathe through their skin, and use hair-like structures to move through the soil, and survive even if part of their tails breaks off.
The book shows how earthworms eat soil and small living and dead things in the soil, and how this makes the soil better for all plants and animals. It tells how they reproduce and that the greatest dangers to earthworms are moles, birds, and sunlight that can dry out earthworm's skin. Earthworms Underground provides a view of the earthworm in its natural habitat and depicts earthworm structures and behaviors that are not directly observable.