an eversible forked pouch in Papilionidae located middorsally on the prothorax.

The fleshy organs protruded by swallowtail caterpillars that produce a strong odour.

A gland bearing strongly smelling substances, usually forked and everted typically from behind the head. plural: osmeteria.

A Y-shaped gland located behind the head of some caterpillars which can be pushed out to emit a chemical disagreeable to potential predators.

Fleshy organ that can be extended from behind the head by swallowtail caterpillars that emits an unfavorable odor to fend off predators

fleshy structure on some larvae, often discharging odorous chemicals

An osmeterium is an orange, y-shaped gland on the neck of some caterpillars. This gland gives off a strong, unpleasant odor when the caterpillar is threatened, keeping away dangerous wasps and flies that try to lay eggs in the caterpillar. Many swallowtails have an osmeterium.

The osmeterium is a fleshy organ found in the larvae (caterpillars) of Swallowtail butterflies. This organ emits smelly compounds believed to be pheromones. Normally hidden, this forked structure can be everted when the caterpillar is threatened, and used to emit a foul-smelling secretion containing terpenes.