A novel monoterpene, 2(S), 3(S)-epoxy-3, 7-dimethyloct-6-enal (1), was isolated from the opisthonotal gland secretion of the mite Tyrophagus perniciosm, and was synthesized by asymmetric epoxidation of nerol with subsequent oxidation by pyridinium dichromate. The presence of this compound is a striking feature for chemical taxonomy since it has not been found in morphologically similar mites.