You can find C. elegans worms feeding on bacterial blooms in decomposing fruits and stems. This review of the natural history of C. elegans by Lise Frézal and Marie-Anne Félix is excellent.

The Natural History of Model Organisms: C. elegans outside the Petri dish

To leverage the tools, resources and knowledge that exist for C. elegans so that we can study ecology, evolution and other aspects of biology, we need to understand the natural history of this importa...

thanks this is great! i had asked the grad student where c. elegans was, way before 2000! alas it does not appear to be found in ny or new england where i live. pity. maybe other Caenorhabitis spp? weird. two samples in canada north of me tho