Life Cycle of the Black Swallowtail Butterfly (Papilio polyxenes)
By Sharon Gray, Master Gardener in Training
The black swallowtail butterfly is one of the most beautiful butterflies to be found here in Manitoba. Female swallowtails, identified by larger, more prominent blue markings, and lesser yellow markings are larger than males. The butterfly has a wingspan of 69-84 mm (2 3/4 – 3½ inches).
Female Swallow, Photo by Prof. Donald W. Hall, University of Florida, Dept. of Entomology & Nematology, used with permission
Male swallowtails are identified by the lesser blue markings, but larger yellow markings on the upper part of their wings.
Male Swallowtail, Photo by Prof. Donald W. Hall, University of Florida, Dept. of Entomology & Nematology, used with permission
The swallowtail also has distinct markings on the underside of its wings, and a prominent tail.
Swallowtail Wing Underside, Photo by Prof. Donald W. Hall, University of Florida, Dept. of Entomology & Nematology, used with permission
It is found throughout most of North America, and is one of many species in the butterfly family, called Papilionidae. It ranges from southern Canada to northern South America, but is most common east of the Rocky Mountains. It is the state butterfly of Oklahoma and New Jersey.
Unlike the monarch butterfly, it does not migrate, but can overwinter in the pupa (chrysalis) stage, eclosing (emerging) in the spring. The overwintering pupae are brown and are not always easy to find. When they eclose, the female will lay eggs on the larval host plants, which are mainly dill, parsley, and other plants of the carrot family (Umbelliferae/Apiaceae) like our native heart-leaf Alexander (Zizia aptera). The pale yellow eggs are spherical in shape and darken as the caterpillar develops inside. The eggs hatch in 3 to 9 days, with the caterpillar chewing its way out of the egg, then consuming the eggshell. The first larvae (instar) are spiny and mostly black. The second and third instars are an orange/red colour. Older larvae (fourth and fifth instars) are green with transverse bands of black with yellow spots. They are camouflaged as they feed on the host plant. Here is a photo of a chrysalis that has overwintered:
Black Swallowtail Chrysalis, Photo by Edith Smith, used with permission
Black Swallowtail Egg, photo by Prof. Donald W. Hall, University of Florida, Dept. of Entomology & Nematology, used with permission.
Here are some images of swallowtail caterpillars that I had in my garden this past summer: (Taken July 3, 2020).
Note the ‘feet’ holding on to the dill branch.
I had multiple caterpillars in my garden, as I have dill that comes up everywhere, even in my flowerbeds. I counted about 10 one day.
These caterpillars are getting ready to form into a chrysalis.
I could not find the chrysalis anywhere (the are not easy to find), but I came home from work one day and found this swallowtail just resting on my tomato plant. I believe it had just hatched, as the date was July 17. It was very still, for a long time.
Black Swallowtail on tomato plant
The life cycle of the butterflies that hatch in the spring/summer is approximately 6-14 days. They will lay eggs after hatching, approximately 200-430 in total. The eggs take 10-13 days to hatch. The eggs will hatch, and the caterpillar will feed on dill, parsley, carrot, and fennel for about 3-4 weeks. They will then find a branch, or twig and form a chrysalis, which will be pale green in color. It will eclose after 10-20 days. This is the first adult butterfly generation. It will then begin the life cycle all over again, with the chrysalis of the last generation overwintering to emerge the following spring. In Manitoba there are only two generations per year.
When forming the chrysalis, the transformation is quite amazing. The caterpillar will find its spot, and hang in a ‘j’ formation for several days before it pupates. The pupating process only takes a few minutes. While inside the chrysalis, changes in the caterpillar cells unlock complex chemical processes responsible for the radical transformation of its body into a butterfly. Scientists (entomologists) can now peer into the chrysalis and watch the transformation as the different parts start to form and grow. The new organs, wings, antennae, and legs form while in the chrysalis stage. The wings are usually visible about 24 hours before it hatches. When they hatch, they are soft, and pump blood into their wing veins, which then harden for flight.