Seasons of the swallowtail butterflies
For many of us in the High Country, seeing beautiful butterflies fluttering through the air, or sitting on flowers, is a welcome site. The numerous species in our area, varying in size and color, are not only aesthetically pleasing but very important for many plants, since butterflies are great pollinators. Particularly striking are the swallowtails. These butterflies have an extension from their wings that give them the appearance of small kites. There are several species in our area, with the tiger, spicebush, and pipevine swallowtails being especially common. In these species you may have a noticed the handsome adults in spring and late-summer, but few or any in mid-summer. This phenomenon illustrates how many insects have "seasons" in their lives. To further explore this, let's examine the life history of the tiger swallowtail, whose large yellow and black striped adults make them easy to identify.
Photo Credit: Becca MacDonald, bugwood.org
The general life cycle of the tiger swallowtail is as follows. Caterpillars (the juvenile stage) hatch from eggs laid by mated females. After feeding on various hardwood tree leaves for several weeks, each caterpillar forms a pupa. The adult butterfly emerges from the pupa and the male and female mate to start the cycle anew. Tiger swallowtail butterflies in our area that are seen in May or June have emerged from a pupa that formed the previous fall. The pupal stage allows the insect to be dormant and survive the whole winter.
Why do we see many swallowtails flying about in May and June, and not again until August or even September? This is because there are two life cycles each year. The eggs laid by females in the spring hatch, and caterpillars feed, as described above. Since adult tiger swallowtails only live one or two months, during the several weeks of feeding by caterpillars over the summer, followed by the pupae forming, no adults are present. Then in August or September the familiar tiger swallowtail butterfly adult emerges from a pupa and appears again. But instead of producing a new generation of adults, feeding caterpillars form the overwintering pupa and the life cycle is paused until the next spring.
The number of generations of tiger swallowtails varies by region, and even year. Though more than two generations are possible in the High Country, what I described above is a more typical scenario. Even though these butterflies are not unique for insects having multiple generations each year, the welcome appearance of these beautiful insects provide an easily recognized example of this phenomenon.
Because swallowtails are important pollinators, you can do your part making sure they have plenty of flowers to retrieve nectar from by planting flowering plants that bloom in spring and late summer. On our property butterfly bush, bee balm and Joe Pye Weed attract many swallowtails. A great resource on plants supporting large butterflies in our region is found here- https://choosenatives.org/articles/nectar-sources-large-winged-butterflies-mid-atlantic. By being "butterfly friendly" you can help assure we'll enjoy the beauty of these fascinating flying kites each year.
Sources:
JM Scriber. 1996. Tiger tales: natural history of North American swallowtails. American Entomologist. 42:19-32
University of Florida
Tiger Swallowtail
https://entnemdept.ufl.edu/creatures/bfly/tiger_swallowtail.htm
Pipevine Swallowtail
https://entnemdept.ufl.edu/creatures/bfly/pipevine_swallowtail.htm