Résumé : The Dufour's gland secretion of C. scutellaris contains a series of C 23 long chain derivatives characterized by the presence of a cross-conjugated dienone linked to either a primary acetate, an aldehyde, or a carboxylic acid function. These compounds further differ from each other by the degree of unsaturation and (or) the position of an isolated double bond in the carbon atom chain. A combination of spectroscopic data and chemical degradations led to structures 1a-c, 2a-c, and 5a-c for the major components of the secretion. The highly electrophilic character of these compounds accounts for their efficiency as contact poisons.