Four canthariphilic ceratopogonid species of the genus Atrichopogon were attracted to cantharidin baits in Upper Franconia (Bavaria): A. oedemerarum Storä, A. trifasciatus Kieffer, A. lucorum (Meigen) und A. brunnipes Meigen. Phenological data show different periods of activity for the most abundant species A. oedemerarum (May, June) and A. trifasciatus (September, October). A. trifasciatus was often observed preying on A. oedemerarum at cantharidin traps or in laboratory experiments. All cailthariphilic Atrichopogon accumulate cantharidin in the whole body. -The flies are chemically protected against Empididae (Diptera) by sufficient amounts of this substance if they had free access to cantharidin in the laboratory. In the field cantharidin functions as a kairomone for Atrichopogon. It guides the flies to their hosts (probably Oedemeridae (Coleoptera)) and furthermore males and females meet at these sites.