Two-years' observation of Athelia arachnoidea lesions in the field showed that they are long-lived perennial structures. In the Sheffield area, central parts of lesions become recolonized by Lecanora conizaeoides only after secondary infection by the lichen parasite Lichenoconium erodens followed by an invasion of the green alga Desmococcus naegelii. A. arachnoidea is active only during the winter months probably as a result of the higher humidity. The role of the sclerotia remains obscure.