A Pair of Swallowtails

by Crystal Cockman

March 17,2016

The trout lilies and trilliums are in full bloom, the turkeys are strutting, the smallmouth are biting, and the butterflies are flitting about in our fields and woodlands. One of the most common butterflies seen in our area is the Eastern tiger swallowtail (Papilio glaucus).

Male Eastern tiger swallowtails are yellow with four black tiger stripes on each forewing.  Females are dimorphic, which means there are two different morphs or forms, in this case that being a yellow morph and a black morph. The yellow morph still is discernable from the male because there is blue along the bottom of the hindwing. For the dark morph, the areas that are yellow in the yellow morph are dark black or gray instead, and there is an addition of two bright orange spots at the ends of the blue on the hindwing.

The Eastern tiger swallowtail is found broadly in the eastern United States from Vermont to Florida and west into Texas. They are found anywhere deciduous forests are located, and have a wide variety of host plants. These include species of ash, cottonwood, magnolia, tulip poplar, wild black cherry, and more.

Another species found in our area that looks similar to the tiger swallowtail but is tied to only one type of host plant is the zebra swallowtail (Protographium marcellus). Zebra swallowtails are closely tied to pawpaws, and are almost always found near these trees. They also prefer corridors of woods along riparian areas such as rivers, lakes, and marshes. As their name suggests, they are white with black stripes. They are found in the eastern United States and southeast Canada. Their range extends from southern Ontario and Michigan, across the coast of the Atlantic to Florida and the Gulf.

The caterpillars of zebra swallowtails are cannibalistic, so females lay eggs one at a time. Eggs are laid on pawpaw leaves or tree trunks. Both tiger and zebra swallowtails lay single eggs. Also similarly, they both possess an osmeterium, a yellow-orange gland that emits a fowl smell to deter predators. Also to prevent predation, the dark morph of eastern tiger swallowtails looks similar to, or mimics, the poisonous pipevine swallowtail.

The zebra swallowtail larvae eat the leaves of the pawpaw because most plant tissues are not suitable to them. The adult however is not interested in the flower of the pawpaw, preferring such flowers as blackberry, blueberry, redbud, and milkweed. Zebra swallowtails are also known to exhibit a behavior called “puddling,” which means gathering together on moist soil or sand to obtain amino acids and salts. They have a low, erratic flight, typically staying between 2 and 6 feet above ground.

You’re much more likely to spot the more common and generalist species of the eastern tiger swallowtail, but keep an eye out for the zebra swallowtail, as well. I’ve seen them occasionally at Low Water Bridge on the Uwharrie River, so that would be a good place to stop and take a look. If you walk along the river a bit, you’ll get to see the blooming trilliums, jack-in-the-pulpits, mayapple, and a variety of other great spring wildflowers. It’s a great time of year to be out in the woods.