Eastern Tiger Swallowtail Butterflies

The eastern tiger swallowtail butterfly (Papilio glaucus) is a familiar visitor to backyards throughout the eastern U.S. Tiger swallowtails are one of our largest butterfly species with wingspans between 3 and 5.5 inches wide. Because they are so large and so brightly colored, they are easily spotted when visiting garden flowers. In Kentucky, we typically see the adults flying from April until September.

While adult tiger swallowtail butterflies will drink nectar from a variety of different flowers, the caterpillars depend on trees for their food. This is good news for people who are torn between having large, mature trees on their property and wanting to plant butterfly gardens because those trees could be providing baby food for the butterflies they want to attract. In other words, they may already have a butterfly garden in the form of their mature trees, even though trees aren’t what we typically picture when we think of a butterfly garden. Common host plants for tiger swallowtail caterpillars include tulip poplar, wild black cherry, cottonwood, birches, and willows.

Male tiger swallowtails are bright yellow with black tiger stripes on the tops of their wings. You can sometimes find groups of male swallowtail butterflies gathered on the ground around mud puddles or other damp spots. This is a behavior called puddling. The butterflies are sucking minerals and other substances out of the damp ground. Males puddle more often than females and are more likely to be found puddling in relatively large congregations.

Female tiger swallowtails can be either bright yellow or dark black. Both female color morphs also have the black tiger stripes on their wings; however, the stripes can be nearly impossible to see on some of the darker females. Unlike their male counterparts, the female tiger swallowtails also have a row of blue spots near the bottom of their lower wings.

Eastern tiger swallowtails will have between two and three generations each year. The males fly around patrolling areas with lots of nectar producing flowers looking for females visiting the flowers. After mating, the females lay one egg per leaf on the leaves of their host plants. The eggs will hatch in approximately 5 to 10 days.

When the brown and white caterpillar first emerges, it looks very similar to bird droppings on a leaf. It’ll continue to look like bird droppings for its first couple of molts. After its third molt, the caterpillar will be green with small eyespots on its tail that makes it look like a snake’s head. If disturbed, the caterpillar can extend a pair of orange organs called osmeterium that are normally hidden within the caterpillar’s body. The osmeterium look like horns or a snake’s tongue and can produce a very stinky odor. All of these adaptations are designed to help protect the caterpillar from predators.

After approximately three to four weeks, the caterpillar will turn brown and will crawl down from the tree leaves where it has been feeding. It will form a brown chrysalis on the tree trunk, usually close to the ground, or mixed in with the leaf litter on the ground. (Eastern tiger swallowtails are one of many butterfly species that forms chrysalises among dead leaves on the ground.) In the spring and early summer, the chrysalis stage will last for 10-20 days; however, late summer and early fall tiger swallowtail caterpillars will remain in the chrysalis stage overwinter. Once they emerge from the chrysalis, adult tiger swallowtail butterflies only live approximately one to two weeks.

Even though the eastern tiger swallowtail is so familiar and easily observed, there is still much that we don’t know about this species or that we are only just learning. For example, in 2002, it was discovered that some of the eastern swallowtail butterflies in the Appalachian Mountains weren’t eastern swallowtail butterflies after all. Instead they were a completely different species of butterfly, the Appalachian tiger swallowtail, which was previously unknown to science. More recently, in 2015, a study was published showing that pollination of flame azaleas happens primarily from pollen transferred on the wings of eastern tiger swallowtails! I’m always amazed and excited by how much we still have to learn about common species like the eastern tiger swallowtail.

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This article was part of Shannon’s original Kentucky Pollinators and Backyard Wildlife blog which evolved into the blog for Backyard Ecology.

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Backyard Ecology: Exploring Nature in Your Backyard
Nature isn’t just “out there.” It’s all around us, including right outside our doors. Hi, my name is Shannon Trimboli, and I am the host of Backyard Ecology. I live in southcentral Kentucky and am a wildlife biologist, educator, author, beekeeper, and owner of a nursery specializing in plants for pollinators and wildlife conservation. I invite you to join me as we ignite our curiosity and natural wonder, explore our yards and communities, and improve our local pollinator and wildlife habitat. Learn more or subscribe to my email list at www.backyardecology.net.