Corticolous mite populations have been analyzed in 3 sites located inn Belgian Lorraine. The Actinedida represent nearly 10 o/o of the arthropods collecte and comprise 54 species among which 22 tydeid mites. The distribution pattern of six tydeid species and sorne other actinedid mites is related to the microhabitat (crustose vs. foliose vs. fruticose epiphytes) and to seasons. The 6 tydeid mites are considered phloiobiontic species. The distribution pattern of 4 Typhlodromus species is also related to the microhabitats. The coexistence on bark of so closely allied species explains through the colonization of different microhabitats (principle of exclusive competition) but other mechanisms such as different foraging strategies should be suspected.