Disturb a swallowtail butterfly caterpillar and you'll see and smell it - the osmeterium. Osmeteria are V shaped tubular glands right behind the head of a swallowtail caterpillar (larva), located on the prothorax. Osmeteria secrete a strong odorous fluid that is assumed to be defensive. Different species osmeteria are different colors.
Gold Rim / Polydamas
It was with some shock that we discovered that out of the about 40,000 butterfly and related photos, we do not have photos of each swallowtail species osmeteria. As soon as we take the rest of these photos, we'll add one for each species found in Florida that are legal to raise.