Lichens represent a complex life form characterized by a symbiotic partnership between at least two organisms: a fungus and an alga. In this unique relationship, the fungus offers a protective habitat for the alga, which, in turn, harnesses energy from sunshine, water and air to provide sustenance for the fungus. They fulfill ecological roles as a food source for many invertebrates and serve as the basal trophic level for a variety of animals, being considered micro-ecosystems which can host a rich and diverse biota. Nematodes are among the most widespread and abundant of all metazoans, inhabit moist interstitial environments in all habitats and are abundant in marine and freshwater benthic habitats and in the soil. They were also reported from accumulations of detritus in leaf axils, in the angles of tree branches and in mosses and lichens. In this case study, the trophic role and diversity of free-living nematodes associated with lichens were examined in an area of Buenos Aires province, Argentina, revealing seven genera of nematodes linked to Heterodermia diademata, representing all trophic levels of free-living nematodes: bacteriophages (Plectus and Acrobeles), fungivores (Aphelenchus), herbivores (Helicotylenchus), omnivores (Eudorylaimus and Mesodorylaimus) and a predator (Prionchulus).