© 2014 The Mycological Society of Japan. A new species of the genus Rickia is described on ants of the genus Messor based on collections from Greece and France. Rickia lenoirii is distinguished from Rickia wasmannii by the smaller size of the thallus and by the fewer number of cells in each of the three series, as well by other characteristics. The newly described species belongs to the perlata morphological group and because of its diminutive thallus may be compared with similar small species, mostly on mites; therefore it could be included among acarophilous forms according to an old Thaxter definition. The database of ant-Laboulbenial interactions consists of 43 species, 10 genera, and three subfamilies of ants documented as hosts for the six Laboulbeniales known from ants worldwide. Some ant Laboulbenial species show a low host phylogenetic specificity while other species are much restricted in their host range. The highly biased known distribution of ant Laboulbeniales is probably an artifact and the database is far from being complete.