When we moved to Jefferson County last summer, we were thrilled to discover zebra swallowtail butterflies.
I had seen zebra swallowtails before and had long admired them. Smaller than the big yellow tiger swallowtail, the zebra has sharply triangular forewings, dramatic tail streamers, and a bold, racy pattern of black and white. The white seen up close is actually very pale green. Two crimson and two blue spots adorn the hind wings just ahead of the streamers, and two crimson stripes run along the underside of the hind wings. All these longitudinal stripes enhance their streamlined look. Their beauty is unsurpassed. When half a dozen zebra swallowtails land close together in the wet mud near our mailbox, it looks like a butterfly bouquet.
Despite their racy appearance, zebra swallowtails lack the darting, dodging flight of the larger swallowtails. The zebras tend to travel about two feet off the ground in a steady but labored flight—as if their long tail streamers slow them down.
Zebra swallowtails depend upon pawpaw trees. They fasten their eggs onto young terminal pawpaw leaves in the spring. These eggs hatch into caterpillars with a smooth, tapered shape. And in the zebra tradition, they are striped with narrow bands in an alternating pattern of black, white, and yellow. The markings on these caterpillars make me smile because they remind me of old fashioned “prison stripes.” As the caterpillars grow, their black stripes become pale gray, except for one near the front of the body.
This stripe, just behind the head, marks the spot where the caterpillar launches his only defense. When the young insect is disturbed, two fleshy, yellow horns pop up like tank artillery and release a chemical that repels would-be predators. When the caterpillar is mature, it fastens itself to the underside of a big pawpaw leaf. It sheds its skin to become a green chrysalis. In a few weeks it emerges to unfurl its striped wings in the shade of the protecting pawpaw.
The connection between butterfly and tree is one-sided—the tree doesn’t seem to need the butterfly. The pawpaw blooms just as the earliest zebra swallowtails begin to lay their eggs. But the odd, purple flowers have a scent of rotting meat, which attracts carrion beetles and flies, but not many butterflies. By the time the pawpaw’s mango-like fruits ripen and drop to the ground in late summer, very few adult zebra swallowtails remain to enjoy the juice of the rotting fruit.
By Doug Pifer