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Hi friends, I hope you’re enjoying the butterflies this summer. Have you seen any of these distasteful beauties?

It was a sunny April afternoon. I was exploring an open woods of oak, hickory, and ironwood near the Broad River in the piedmont of North Carolina. A large velvety black butterfly with flashing metallic blue hind wings caught my eye. It was flitting along near the ground. There were no flowers in bloom in the area but this butterfly was flying up to every young green shoot–honeysuckle, aster, grass, tree seedlings, etc. It wasn’t landing on these plants; rather it flew from one plant to another, spending a second or two at each sprout as if it was checking it out. The butterfly sailed right by taller plants and bushes, pausing only at delicate shoots between about two and four inches in height. This butterfly was on a quest for a rare herb.

This was a gravid female pipevine swallowtail (Battus philenor) ready to lay her eggs. These butterflies are so named because their larvae feed only on various species of pipevines. She was searching for Aristolochia serpentaria, the traditional medicinal plant known as Virginia snakeroot. As an adult butterfly she can sip the nectar of many different flowers, but her young can only feed on members of the Aristolochiaceae family, and in this region Virginia snakeroot was her only choice. I watched her start hovering excitedly around one particular delicate sprout with three, light green, unfurling leaves. No doubt she was receiving chemical/olfactory confirmation. “Yes! Finally, I’ve found it!” her rapidly fluttering wings seemed to say. While her wings kept her airborne, her legs reached out and grasped the plant. The tip of her abdomen briefly touched the stem and there she placed a glistening golden egg that was hardly bigger than a poppy seed. Within a few seconds she was on her way again, continuing her plant-by-plant search for the next snakeroot. I followed her (at a respectful distance) for the next half hour or so as she continued her thorough survey of the forest floor. We may have covered as much as a hundred yards, and she may have inspected as many as a thousand plants as she zigzagged back and forth along the ground. In that entire time she found only that one Virginia snakeroot shoot. She eventually flew up into the canopy and I lost sight of her. This was the first time I had a butterfly as an herb hunting guide!

Although there were obviously enough snakeroots in the area to support at least a small population of these swallowtails, this confirmed to me something I had suspected — that even though Virginia snakeroot has a wide range, (from Florida and Texas north to Missouri, Illinois and southern New England), it is rarely abundant. It is an understated, diminutive herb. Any specimen over a foot tall and having more than ten leaves is considered large. Even in areas of ideal habitat where the plant is relatively common, I never see it growing thickly in beds or patches — just an occasional solitary plant here and there. Even the pipevine swallowtail I followed who had dozens of eggs to deposit seemed to instinctively understand the plant’s limited growth habit. She only placed one egg on that plant. A single plant like this could barely support even one caterpillar. Less than a hundred miles from here, up in the higher mountains on the huge Dutchman’s pipe vine, (Aristolochia macrophylla), I have seen where the same kind of butterfly had laid more than a dozen eggs on one leaf.

The Dutchman’s pipe is as robust and lush as its cousin the snakeroot is sparse. A mature Dutchman’s pipe vine has hundreds of heart-shaped leaves measuring almost a foot across. The vines can be seen festooning the tree tops in rich Appalachian mountainsides as far north as Pennsylvania and New Jersey. The females deposit the eggs in clusters on the stems and undersides of tender young leaves. When the tiny caterpillars first hatch, they often line up side by side in a group and feed communally for the first week or two. As they get older and larger they tend to spread out and go their separate ways.

I didn’t know what I was seeing the first time I laid eyes on a large pipevine swallowtail caterpillar. It was like a weird, purplish sea slug with rubbery tentacles sticking out on all sides and two rows of yellow-orange spots running down its back. It was calmly munching on a large tender Dutchman’s pipe leaf. When I poked it, a pair of slimy yellow horns oozed out from behind its head and I noticed a strange bitter odor. In a few seconds the “horns” were pulled back into the head and they disappeared. These horns are actually a gland called an osmaterium and the odor serves as a repellant to parasitic wasps and other predators.

The caterpillars shed their outer skin several times as they grow. When a caterpillar is ready to pupate, it usually crawls some distance onto a tree trunk or branch. There it spins a silken pad for its hind end (the cremaster), a silken sling around its middle, and sheds its skin for the last time as a larva and it becomes a greyish-tan speckled chrysalis. When the pupation is complete, the chrysalis splits along the back and a soft, soggy adult butterfly emerges. Within an hour or two its wings expand and harden and it flies off in search of nectar and a mate.  Depending on the climate, there may be several generations a year, and in subtropical areas the butterflies sometimes overwinter as adults. The adult swallowtails have a pungent, penetrating odor and disagreeable taste which is believed to come from chemical compounds in the pipevine. This is similar to the monarch butterflies that derive their protective chemistry from compounds in the milkweeds that their larvae feed upon. In much the same way that the viceroy butterfly may have evolved as a mimic of the monarch, it is believed that other butterflies such as the red spotted purple, the female Diana, and the dark phase of the female tiger swallowtail (which are about the same size as the pipevine swallowtail with dark forewings and blue on their hind wings) may have evolved as mimics of the pipevine swallowtail. They all may gain a survival advantage by resembling their foul-tasting cousins.

The yellow and black striped tiger swallowtail is one of the most common and familiar butterflies in the East. I was surprised to learn that some females are almost all black with blue on the hind wings. These dark females have a selective survival advantage in areas where there is also a population of pipevine swallowtails. Since they resemble the distasteful pipevine swallowtails they are less likely to get preyed upon than their yellow “sisters”. But even though the dark swallowtail females have the survival advantage and are more likely to reproduce successfully, the males still mate more frequently with the yellow females. So even among the butterflies it seems that gentlemen prefer blondes and perhaps blondes have more fun.

Even Darwin investigated the question of whether blondes have more fun!

 

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