The defensive osmeterial secretion of pre-final instar larvae of the citrus swallowtail,Papilio demodocus (Lepidoptera: Papilionidae) was found to contain methyl 3-hydroxybutanoate, 3-hydroxybutanoic acid, -pinene, myrcene, limonene, -phellandrene, (Z)-ocimene, (E)-ocimene, -caryophyllene, (E)--farnesene, and germacrene-A, as well as a further number of unidentified sesquiterpenoid constituents. The presence of germacrene-A in the secretion was inferred from the formation of -elemene under certain GC conditions. Larvae of the second, third, and fourth instars produce qualitatively similar secretions. Remarkable quantitative differences were found between the secretions of individual larvae. These variations could not be correlated with the diet on which the larvae were fed, their sex, instar, or color form. However, in a number of larvae the two prongs of the osmeterium were found to produce quantitatively different secretions.