Defensive Secretion of a Caterpillar ( <i>Papilio</i> )

Abstract

The eversible cervical gland (osmeterium) of the caterpillar of the swallowtail butterfly, Papilio machaon, produces a secretion containing isobutyric and 2-methylbutyric acid. The gland is effective in defense against ants. Even when caterpillars were fed on one of three unbelliferous plants (fennel, carrot, parsnip) the secretion contained the same two acids.