Papilio polyxenes Fabricius
Fully developed caterpillar
Black Swallowtail caterpillars have an orange fleshy organ (called the osmeterium) found in the prothoracic segment of caterpillar.
This organ emits odorous 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.
These chemicals vary from species to species. Although it has been postulated that the secretions of the osmeterium are to ward off potential predators,
I have found no definitive data to support that hypothesis.
Auburn, Alabama