Tag Archives: black swallowtail

Papilio polyxenes and the Forked Tongue

Black swallowtail with osmeterium extended, Austin, Texas, 22 May 2010

I promise.

Here is my last photo of a caterpillar for the near term (near term being tomorrow morning). But this is worth studying. The orange forked tongue-like organ is the osmeterium. This is a fleshy organ found in the caterpillars of the swallowtail butterflies. The osmeterium is only extended when the caterpillar is alarmed. When extended the organ emits smelly compounds believed to be pheromones, and the makeup of those pheromones differs from species to species. I cannot describe the smell; like chicken?

Food!

Black swallowtail on parsley

My yard is a feeding frenzy, an orgy of young and old, big and small, eating their ways toward winter. As I walk along my flower beds I hear the constant crunch of caterpillars, ants, pill bugs, and grubs making short work of my crops. The bird feeders are crowded with parents cramming the gaping mouths of young with masticated seeds. Never mind that the young downy is larger than the adult; instinct always wins out over common sense.

Downy woodpecker (adult male)

Doesn’t he know that this young bird is a bottomless pit, an empty hole that can never be filled? No wonder he has brought the family to the McDonalds of the bird world – my feeders. Supersize it.

Downy woodpecker (juvenile) Austin, Texas, 21 May 2010

Supersized are these final instar black swallowtails, moments away from tranforming all of my dill and parsley into an ephemeral butterfly. All that work, all that herb, for a few days of ebony bliss.

Black swallowtail

Swallowtails begin as caterpillars that look like bird droppings. They will go through four molts, which represents five distinct instars. The first three are covered with spikes with a bird-drop white ring in the middle. Only in the final two instars do they swell into the sausage-shaped caterpillars that are obvious on your crops.

Black swallowtail (3rd instar), Austin, Texas, 21 May 2010

In this next photograph the caterpillar, now a 4th instar, has molted its 3rd instar exoskeleton and is drying in the sun. During this brief period the caterpillar will expand its size with air so that when the exoskeleton dries there will be room inside to grow. After the final instar the caterpillar will defecate one final time, passing not only waste but its entire digestive tract. As an adult the butterfly will nectar but not feed. The gut will not be needed.

Black swallowtail (4th instar) after molting, Austin, Texas, 21 May 2010

Are you interested in low-impact, sustainable recreation? Discover your own yard and its inhabitants. See what might be found in the exotic world of your own community.

Black swallowtail chrysalis, Lone Star Lakes, VA, 8 Aug 2001