feider’s work with mites and ticks became very well known abroad, and more specialists in the field were interested in his work. he carried out the taxonomical and systematical study of many acarina groups: ixodoidea, oribatidae, gamasidea, rhinonyssidae, erythraeidea, and prostigmata from romania; nicolletiellidae and sternostoma genus throughout the world. he found phylogenetic indicators in the structures of trichobotrias, aspis, and genital and anal plaques in the larva chetotaxis and visual organs at ixodidae or in the breathing apparatus, metopic edge and genital structure of trombidia.