(Photo By Steve Scott)
Black Swallowtails (Papilio polyxenes asterias), are one of the most common swallowtails found in the Midwest. I see these gorgeous flying flowers with great frequency in our backyard gardens. They nectar at the coneflowers, milkweed and even thistles. They are not the largest of the swallowtails found in Missouri, that prize goes to the Giant Swallowtail, but they certainly are one of the prettiest. They have a wingspan of up to 3 1/4 inches, which is no small butterfly by any means. They are mostly black (hence the name), but they have a delightful array of bright colors like yellow, blue and orange along the edges of the wings and at the base of the "tails". The underside is also made up of these beautiful markings, as you can see in the 4th picture.
They can be found in a variety of habitats, including backyard flower gardens, vegetable gardens, open fields, desserts, marshes and along roadsides. Late in the spring males will begin seeking females. They perch from some vantage point and wait for receptive females to come into view. Once mated, the female will then lay her eggs singly on the leaves of the host plant. In the case of these butterflies it is plants in the Carrot family, including Dill, Fennel, Celery, Queen Anne's Lace, and even occasionally plants in the citrus family will be used such as lime, lemon, orange and grapefruit. The eggs are tiny and round in shape and may be found both on the underside and the upperside of the leaves of the host plant. When the eggs hatch the newly emerged caterpillars are very tiny and would fit between these parenthesis ( ). Because of this incredibly tiny stature they often go unnoticed. Look carefully among the foliage of your dill, parsley, fennel or in the wild Queen Anne's Lace. Although they are present all summer it seems that the best time to find them in NW Missouri is in August or September.
The two caterpillars pictured here are feeding on dill. I plant it each spring just by scattering the seeds randomly throughout my gardens. The lacy leaves and tall stalks make for interesting contrasts between the flowers. Walking through the garden, and brushing up against the dill releases a pungent, yet fragrant aroma completely unique to dill. Each summer I am rewarded with numerous black swallowtail caterpillars all munching away at the foliage.
This butterfly is considered a Pipevine Swallowtail mimic which are a poisonous butterfly. They use chemicals they acquire from the plants they feed on as a caterpillar. This toxic brew of chemicals that the plant gives off is harmless to the caterpillar, but gives the caterpillar and later the butterfly it becomes a chemical defense against predation.The Black Swallowtail is not known to be poisonous, but it so closely resembles it's poisonous cousin that this affords them some protection from predation by birds and other hungry creatures.
If you want to attract these beautiful caterpillars and butterflies to your garden....plant dill, fennel, carrot or Queen Anne's Lace for the females to use as a host. Then plant plenty of bright flowers like coneflowers for the adults to nectar at, and you should see them with the first rays of summer sun.