Glands of the 4th and 5th abdominal stemite of the caddis flies Potamophylax latipennis, Potamophylax cingulatus, and Glyphotaelius pellucidus contain (S)-4-methyl-3-heptanone (4a), (4S,6S)-4,6-dimethyl-3-octanone (4b), and (4S,6S)-4,6-dimethyl-3-nonanone (4c). As shown by gas chromatography coupled with electrophysiological recordings, these ketones elicit a strong response in the insects' antennae. The structural assignment of the compounds was achieved on the basis of mass spectra, enantioselective synthesis, and gas chromatography on a chiral stationary phase.