They're the most common multi-cellular animals in soil. And they live all over the world. Roundworms also live as parasites in animals, including people. They aren't related to earthworms at all. Don't be fooled by their plain looks.
Nematodes feed at every level of the soil food chain.
This species hunts for bacteria. It swallows them whole and digests them in its gut. Other kinds of soil roundworms eat dead organic matter. Some prey on protozoa and other nematodes. Still others eat fungus.