Spicebush swallowtail: Master of disguise
By Shelley Tender, Interpretive Services Manager
Our Ohio landscape is graced by the presence of six different species of swallowtail butterflies. These delicate, beautifully decorated creatures belong to the family of butterflies known as Papilionidae, which contains more than 550 species worldwide. The majority of these large lovelies are tropical, but every continent except Antarctica is fortunate to have several representative species.
In my opinion, the spicebush swallowtail butterfly (Papilio troilus) is one of Ohio’s most beautiful and interesting swallowtails. Its name is derived from its most common host plant, the spicebush (Lindera benzoin), and it is relatively common in natural areas and flower gardens throughout the eastern and parts of the mid-western United States.
Spicebush swallowtails are masters of deception and camouflage in every stage of their lifecycle. As adults, they exercise Batesian mimicry by resembling a distant relative — the pipevine swallowtail. Pipevine swallowtail larvae feed on plants that contain aristolochic acids. The ingested acids are passed on to future butterflies through each of their life stages and make them distasteful to predators. By adorning a similar color pattern, the spicebush confuses its potential assailants and is provided some protection from being preyed upon.
But the deception doesn’t end there!
After mating, females lay single eggs on the underside of host spicebush or sassafras plant leaves. As they exit their eggs, the diminutive hatchling caterpillars set to work devouring as much of the leaves as they can and continually growing through five stages called instars. Between each instar they stop eating, shed their outer skin, and get larger. Instars one through four are cleverly camouflaged by way of resembling bird droppings. As if that wasn’t protection enough, they have the ability to hide themselves in cozy leaf shelters they make themselves. They do this by exuding silk from their body and stretching it out along the midrib of the leaf. As the silk dries it contracts, causing the leaf to curl over the larvae. Talk about being snug as a bug in a rug … wow!
The fifth and final instar isn’t content to keep its juvenile wardrobe, opting instead to turn a bright green color and sporting a swollen thorax and large false eyespots. In so doing, it achieves a snakelike appearance.
If the clever camo and sheltering in place do not work, they have yet another defense mechanism to employ. At each of the larval stages, they are equipped with a set of bright yellow-to orange horn-like organs called osmeteria. When threatened, the larva rear up and smear the potential predator with a chemical repellent. Ugh!
As the final instar larva prepares for pupation, it dons another cryptic disguise. The caterpillar turns a muted orange-yellow color. It is believed they do this to more closely resemble the leaf litter that it crawls around on when looking for a suitable site in which to anchor itself before forming the chrysalis.
But wait … there’s more! To stay consistent with its trickery, the chrysalis itself resembles a leaf. I think it is safe to say the spicebush swallowtail wins the costume contest, don’t you?
