What is that stinky orange thing?
When touched, swallowtails evert (stick out) a moist, forked, bright orange gland called the osmeterium. The moistness comes from terpene excretions, which stink. The bright color and strong smell are thought to startle predators. When not extended, the osmeterium folds in on itself in much the same way as a water snake toy works. Do early instar forms also have osmeteria? We had previously thought only the later (green) instar stages had osmeteria, because that was the only stage at which we had seen them. This year we observed some very young larvae (probably 2nd or 3rd instars) using their tiny osmeteria. What happens if the osmeterium touches me? You won’t be harmed, but the part of you it touched will stink! No worries, though, it washes right off. Why do they spit? One caterpillar in our garden produced a greenish liquid from its mouth when provoked into extending its osmeterium. We were able to reproduce this reaction with the same caterpillar, but never witnessed it in another
