Life Styles of the Scaled and Beautiful: Pipevine Swallowtail 

By Jim Brock

The following article originally appeared in American Butterflies (Vol 9: No.1, Spring 2001).

Okay, let’s be honest out there. How many of you occasionally make some neat butterfly discovery while not actually intending to be out butterflying? You know. You’re out shopping, on an errand, or picking up the kids at school and you stumble upon something new, whether it’s butterfly flowers in someone’s yard, a colony of host plants you didn’t know existed or you even run across some rare, stray adult butterfly of some kind or another. I know it happens right in your own neighborhood.

One of my more exciting finds occurred while walking my dog, Doogie, around the block one morning. This is a walk that we  frequently take, but this

Pipevine Swallowtail nectaring.
Pipevine Swallowtail nectaring.

particular summer morning Doogie saddled up to what was a new tree for him. He stopped, sniffed and passed on this particular tree.

But while standing there I thought I recognized a dense, basketball sized mass of leaves piled up at the base of this catclaw acacia tree. Upon closer inspection my hunch was correct. It was a huge, native pipevine plant! A “monster” plant! I have seen many a pipevine of this species (Aristolochia watsoni) in the Southwest but never one of this magnitude and certainly never in my neighborhood. I had walked this route easily a hundred times before. It’s an exciting discovery! Good going, Doogie!!

I began to examine the leaves and to my astonishment there were four young Pipevine Swallowtail caterpillars sitting on the plant! This was interesting to me for two reasons. One, I had pipevine in my yard nearby but had never had caterpillars in three years of residency. Two, I had no idea the plant occurred naturally in my neighborhood. I was of the opinion it was only found in relatively undisturbed areas in the hills a few miles from my home. There are some natural desert areas nearby but the understory is generally sparse since most of my neighbors prefer to “clean out” the desert leaving mostly just the trees.

I was injected with new optimism. It really was possible to have early stages of the Pipevine Swallowtail in my yard. In fact, I lived in a breeding area!

The early stages of the Pipevine Swallowtail are spectacular and well worth gardening for! The eggs are red-orange and laid on the freshest tips of the plant. One often finds them clustered together further reaffirming the female’s intent to place them on the more tender bits of foliage.

The early stage caterpillars can also be found clustered together. As they get older they become more solitary although one often finds small numbers of them close together.

Mature caterpillars are either bright red or purplish-black and about two inches long. There are two rows of fleshy bumps down the back with a long pair of filaments arising just behind the head and flaring out to the side. On purplish-black forms the bumps are either red or orange while on red forms the bumps are usually the same color as the body. Along the sides there are more fleshy bumps, the first three pairs are more like filaments and about half as long as the long filaments behind the head. Overall, the early stages are like warning beacons. Bright colors advertising to potential foes “Don’t eat me!”

If that weren’t enough protection swallowtail caterpillars also possess an osmeterium. This is a retractable fleshy organ behind the head that is extruded when the caterpillar is alarmed. It releases a strong pungent odor that supposedly drives off potential enemies.

The chrysalid is more subdued in color than the caterpillar. It is brown or green with bright yellow markings. The head end has two points and there are small plates down the back where before there had been bumps. These plates remind me somewhat of that dinosaur known as a Stegosaurus.  The chrysalids are attached to some object (usually a wall, tree or shrub) at the abdomen and the rest of the body is suspended, supported by a silk strand wrapped around the back and attached to the object on either side. I have heard of concrete slabs, bridges and overhangs in northern California where hundreds of chrysalids hang suspended.

Scientists have determined that pipevine plants contain chemicals that when ingested by the caterpillars make them poisonous. It is supposed to provide the caterpillar protection from predators. Perhaps this is why one often finds the caterpillars resting out in the open. There is no need for concealment if one is normally left alone.

There is another reason why Pipevine Swallowtail caterpillars are found just sitting out in the open on the ground or on grasses or shrubs unprotected. Many of their host pipevine plants have small leaves and are unable to provide enough food for even a single caterpillar. So the caterpillar must fend for itself and locate other plants in order to survive. One can play detective and try to locate the nearest pipevine. But the next question is, how does the caterpillar locate another plant? Is it by random chance or is it found by sensors located somewhere on the body? How long can it go without feeding?

Hmmm! Perhaps I can actually test this in my own backyard and get answers. Maybe some day I’ll find that a female has blessed my pipevine plants with eggs. Do the eggs get attacked or are the colors enough to protect them? Are all predators deterred from eating the caterpillars or does some fiendish beast find them delightful to the taste and palatable to its stomach?

There are perhaps as many as three generations per year in some areas of the country. In my neighborhood Pipevine Swallowtails fly from February to November. This extended breeding season would seem to create a greater potential for getting caterpillars in my yard. However, for some reason I haven’t been getting any caterpillars. That is, until the summer of 2000.

In between field trips last summer I was checking out one of my nectar plants that was apparently not getting enough water. While examining the plant I noticed five red Pipevine caterpillars on the very first pipevine that I planted in my garden. They were already a little more than half-grown. Finally I had some success! It was a little disappointing to have not been around to see and count the eggs. Still, this was a victory and I planned on taking their pictures in a couple of days after they had grown a little larger.

I returned to the plant a few days later and they were gone! There wasn’t a trace! They would not have been fully grown after just two more days of feeding. Some dastardly beast must be to blame! Now this really is intriguing. Even with the bright colors, osmeterium and potentially lethal body fluids something may have made a meal of these wonderful caterpillars! It looks like my backyard detective work has only begun.

Perhaps many of you have observed Pipevine Swallowtail caterpillars or adults in your butterfly gardens. Others may wish to add this plant to their botanical repertoire. I collect seed from my existing plants when the opportunity arises and throw them around my property. The more pipevine gardeners we have the better chance of someday solving these mysteries. As for me, I can’t wait for the Pipevine Swallowtails to begin their season. In the meantime I think Doogie and I will go looking for more pipevines.

Good boy, Doogie!