While exploring the backyard with my son the other evening, a large yellow-orange caterpillar with huge spots that looked like eyes captured our attention. It was slowly meandering through the low-hanging vegetation of our sassafras tree. What we were looking at was the last instar of the spicebush swallowtail caterpillar (Papilio troilus), right before the larva pupated and would later emerge as the gorgeous large black butterfly.
The spicebush swallowtail butterfly has a wide range that is commonly found in regions east of the Mississippi River. Its black wings, with a wingspan of nearly 4 inches, have ivory and blue spotting along the lower margins, though it’s not all that visually distinct from several other native butterflies in the same range. It looks much like the pipevine swallowtail, which is black with similar coloration. This is intentional.
The larval and adult forms of the spicebush swallowtail employ a number of morphological and visual strategies to avoid being consumed by birds and other common predators. Because the pipevine swallowtail is toxic to many predators, birds and other species will avoid eating the them and, by association, any butterflies that look like them. But this isn’t their only defense mechanism—in every stage of the butterfly’s lifespan, it employs effective means of camouflage to keep predators at bay.
The first instar of the spicebush caterpillar is greenish-brown with white splotches, which realistically mimics bird droppings. The later instars of the caterpillar are bright green with two huge eyespots near the front of the insect, giving it the appearance of a small green snake, especially when the caterpillar is partially concealed in a wrapped leaf. The orange color of the caterpillar my son and I encountered only occurs in the last few days before the caterpillar constructs a leaf-like pupa.
A Garden Good Bug
The great news for gardeners is that the larval forms of the spicebush swallowtail don’t feast up the crops in our garden—they prefer the fragrant foliage of plants in the Lauraceae family, which includes sassafras, spicebush and sweetbay. As an additional boon, the adult spicebush butterflies help pollinate a number of native species in their wide geographic range. To encourage spicebush swallowtails in your garden, plant some sassafras or spicebush and keep a sharp eye out for the amazing larval forms of this butterfly.