Toxic Beauty

One of the most common butterflies in West Virginia, including the New River Gorge region, is also one of the showiest. The pipevine swallowtail, Battus philenor, is a winged work of art, a fluttering gem glazed in psychedelic blue iridescence and stippled with neon orange dots below. When sunlight glances off the upperwings, the butterfly explodes in a shimmering burst of electric azure.

Butterflies and plants are inextricably linked. Flowers rich in nectar, such as milkweeds, entice the butterflies to feed. Nectaring butterflies, gracefully flitting among flowers, are the most visible part of the butterfly life cycle: egg, caterpillar, chrysalis, adult. But it is the caterpillars that do the heavy lifting, and dictate where the butterflies occur.

Pipevine swallowtail caterpillars are eating machines. Plant matter is continually vacuumed in one end, and emerges from the end in the form of little pellets known as frass. Most butterfly caterpillars are finicky eaters; the pipevine cats especially so. A plant that is required sustenance for a particular type of caterpillar is termed a host plant. Pipevine swallowtail caterpillars only eat members of the pipevine family of plants. In West Virginia that is mostly the high-climbing Dutchman’s pipevines. Nearly all of West Virginia’s some 2,500 species of butterfly and moth caterpillars are excluded from eating pipevines due to their toxicity. For you and me, eating the foliage of these plants would be akin to noshing on salad laced with arsenic. Pipevines are infused with aristolochic acid, which is very toxic stuff. As the swallowtail caterpillars have evolved the ability to assimilate the toxins and sequester them in their bodies, the caterpillars in turn are highly distasteful. Caterpillars are nature’s hotdogs, and legions of predators seek them out for food. Not so much the pipevine cats, though.

The distasteful effects of aristolochic acid carry through to the adult butterfly, and they too are shunned by most predators. This has spawned a phenomenon known as Batesian mimicry, in which tasty animals evolve the appearance of toxic ones. Several other butterflies, including the red-spotted purple and spicebush swallowtail, resemble the pipevine swallowtail to a great degree. Presumably the harmless species gain a measure of protection by their mimicry. Birds, especially, quickly learn to shun distasteful food sources. The most interesting of the Batesian mimics is the eastern tiger swallowtail. These large yellow and black butterflies can’t be missed, and males look nothing like the dark pipevine swallowtails. But in regions where pipevine swallowtails abound, such as the New River Gorge, a large percentage of female tiger swallowtails are black and greatly resemble the pipevines. Apparently nature only invests in protective coloration for the female butterflies, as they play a larger role in carrying on the species.

Pipevine swallowtails are fond of forming “puddle clubs.” Aggregations of butterflies often gather in areas of damp soil. These groups are comprised of males; they tap salts from the soil which are essential in replenishing their reproductive secretions. Swallowtails often visit flowers as well, but photographers soon learn that they are tricky subjects. Pipevines nearly always flutter their wings, as if caught in a breeze, making it difficult to freeze the action.

If you want pipevine swallowtails in your yardscape, plant some Dutchman’s pipe around the home. Chances are good that the butterflies will lay eggs which will spawn caterpillars. Plant some milkweeds and other native plants in the garden and you’ll soon have a constant procession of beautiful butterflies dropping by.

Jim McCormac is an Ohio-based naturalist, author of three books on wildlife, and frequent blogger at jimmccormac.blogspot.com.

Tags: wildlife

Category: Nature