(+)-Menthol was mixed in an artificial diet at a concentration of 1 mg/g of diet, and the diet was fed to the last instar larvae of common cutworm (Spodoptera litura). Metabolites were recovered from frass and analyzed spectroscopically. (+)-Menthol was transformed mainly to (+)-7-hydroxymenthol. Similarly, (-)-menthol was transformed mainly to (-)-7-hydroxymenthol. The C-7 position of (+)- and (-)-menthol was preferentially oxidized.