A nitrogen-containing terpene 6,6-dimethyl-2-azaspiro[4.4]non-1-ene (polyzonimine) was isolated from the defensive secretion of the milliped Polyzonium rosalbum. Polyzonimine, which is repellent to such natural enemies of the milliped as ants, acts as a topical irritant to insects (10-4 M induces scratching in cockroaches). Its structure was confirmed by a five-step synthesis starting from 2,2-dimethyl-7-oxabicyclo[4.1.0]heptane.