Good friend, Judi Thorne, called May 31, to report an event we've been watching for six years after a resident brought me two very large caterpillars to identify. They were both brown and white blotched, looking like huge bird droppings, perfect disguise for Giant Swallowtail butterfly caterpillars.
I knew Judi and her husband Rick had two mature citrus trees, an orange and lemon tree, in their back yard, host plants for the Giant Swallowtail. Judi was excited to play godmother to the butterfly caterpillars. She knew damage to her citrus trees would not even be noticeable.
Most butterflies have a strategy of laying only one or two eggs per plant or per leaf, and host plants are seldom damaged to the point that functions and growth are interrupted. Monarch caterpillars do tend to chew their host plant, butterfly weed, down to the ground, but the plants grow back to serve the next generation. If you have a small potted citrus tree that might not be able to spare a few leaves, simply transfer the Swallowtail caterpillars to a mature cultivated citrus tree or wild citrus.
Black Swallowtail host plants in the citrus family are mostly wild natives: torchwood, hop tree, box thorn, Hercules club, wild lime. Hercules Club is quite common in this area of Florida, and, given a choice, Giant Swallowtail caterpillars seem to prefer this wild citrus. One year I transplanted two Hercules Clubs, about two feet tall, to the back of my butterfly garden and enjoyed the company of Giant Swallowtails for many years.
When Giant Swallowtail caterpillars reach a fat two inches long, they crawl off and curve into a crescent shape to undergo the final stages of metamorphosis. The pupa is gray and white, disguised to look like the end of a small twig. Time spent in the pupal form varies from weeks to even months or years, depending on weather and other conditions. Under ideal conditions, the adult butterfly may spend only 10 days in the pupal form.
If the pupa becomes transparent and you see the form of wings, pull up a chair and expect to sit a couple of hours to see the emergence of the adult. Early mornings are most common for emergence, but when the butterfly is finally out it must rest and let the wings unfold before it's ready to fly, scattering a small shower of liquid as it goes.