The Eastern Tiger Swallowtail is one of the more common and noticeable butterflies found east of the Mississippi, the Great Plains states and even in several Mexican states. Its four zebralike stripes on each of its forewings cut across a yellow background that can span from 3-5.5-inches from wing-tip to wingtip, with the females sporting the larger size. The Swallowtails gained their name from the extensions on their hindwings which resemble a swallow’s tail. Unlike members of the brushfooted butterflies where the first two legs are undersized, the Tigers’ front two legs are regularly sized. They are a member of the Papilionidae family which includes all the swallowtail butterflies. Curiously, “ glaucus ” is latin for bluish-gray which does not describe the butterfly at all. I surmise it might be named after the artist, John White, who first drew it while on an expedition with Sir Walter Raleigh in 1587.
The female only lives a few days and during that time, after mating, she will lay her eggs on the host plants in the magnolia and rose family namely, Tuliptree ( Liriodendron tulipifera ), Wild Black Cherry ( Prunus serotina ), Sweet Bay Magnolia ( Magnolia virginiana ) and Sassafrass ( Sassafras albidum ). Their eggs are large and green, and can take 4-10 days to hatch. The caterpillars go through five instars before pupating; this pupal stage can take 9-11 days before the adult emerges. There are two broods produced each year, the spring brood, and summer brood. Brown or whitish chrysalids overwinter and emerge in late spring or early summer. This is called the spring brood and is the one that lays eggs to create a summer brood. Occasionally, Tiger Swallowtails will congregate, or “puddle”, around a moist spot on the ground. It is only the males that exhibit this behavior and it is thought that the amino acids and sodium ions they slurp up may aid in reproduction.
The Tiger Swallowtail has evolved to include several types of protection against predators, starting with the larvae. The first three instars look like bird droppings [ Fig 3 ]. For the last two instars, they turn bright green and another deceptive adaptation emerges: the false eyes [ Fig 4 ]. Having a look of defiance could be enough to put off a visual predator; its true head is tucked underneath the body. Continuing with their deceptive abilities, their later instar coloring is an example of “countershading”. This camouflage strategy helps protect them from being detected by visual predators. In art, should the sun be shining on the top of the caterpillar, the underneath would be darker and form a shadow and thereby produce an easy-tospot 3-D form.
In countershading, the coloring of this caterpillar is inverted: the top is a darker color and gradually gets lighter toward the bottom. The later instars also create a mat of silk on which to rest, this mat causes the leaf to partially curl. They will move from this resting site to other parts of the plant to eat then return to take a nap [ Fig 5 ]. One of the cooler defenses this caterpillar, as well as other swallowtail caterpillars posses, is “osmeterium”. [ Fig 6 ] These are the orange “horns” that the caterpillar sticks out when it is disturbed. These glands contain acids that produce an acid which is potent even in vapor form. I can say with absolute certainty that it won’t kill you but will make you want to wash the exposed body part or clothes as soon as possible.
Something that surprised me several years ago when I started taking photographs of these butterflies was that the females can have a black form! Like many butterflies, the Tiger is a yummy morsel so the females use ‘Batesian mimicry’ to protect themselves. Batesian mimicry is a form of imitation whereby the coloring of a nonpoisonous animal is similar to the coloring of a poisonous one, (like the Viceroy butterfly that mimics the Monarch coloring). The black form of the female Tiger Swallowtail is thought to mimic the coloring of the poisonous Pipevine Swallowtail [ Fig 9 ]. The picture in Figure 9 below is of the male and there is a great quantity of blue on the hindwings. The coloring of the female Pipevine is much duller and looks slightly closer to the picture of the Tiger’s dark form. …sort of… Lastly, the adults will drink nectar from a variety of native and exotic flowers and prefer sturdy plants: Dogbane family ( Apocynaceae ), Aster family ( Asteraceae ), Legume family ( Fabaceae ) as well as Wild Cherry, Lilac ( Syringa ), Milkweed ( Asclepias ), and Joe-Pye Weed ( Eutrochium ). Really, it’s their longer tongue length, structure of the flower, and viscosity of the nectar that will influence their decision about what flower to visit. Butterflies in general prefer nectar with a sugar content of about 35-40%. This produces a liquid that is less sticky and more fluid and easier to suck with their proboscis. I spotted them on ( Dipsacus ), Cosmos, Coneflower ( Echinacea purpurea ), Pinklady Primrose ( Oenothera speciosa ), Rosa Rugosa, Purple Dead Nettle, NY Ironweed ( Vernonia noveboracensis ), and Marigold.
I also caught one amongst my ornamental cherry blooms this past April – but I’m not sure it was nectaring as much as basking in the last sun rays of the day.
Text & Photos by Anna Letaw, UME Master Gardener
1. https://www.fs.fed.us/wildflowers/pollinators/pollinator-of-the-month/TigerSwallowtail.shtml downloaded 10-21-18
2. https://en.wikipedia.org/wiki/Papilio_glaucus downloaded 10-21-18
3. https://www.fs.fed.us/wildflowers/pollinators/pollinator-of-the-month/TigerSwallowtail.shtml downloaded 10-21-18
4. Jane Hurwitz, Butterfly Gardening: The North American Butterfly Guide (Princeton: Princeton University Press, 2018) 63.
5. Hurwitz 36
6. http://www.dartmouth.edu/~mpayres/pubs/Lederhouse_etal_1990.pdf downloaded 10-21-18
7. Thomas Eisner and Maria Eisner and Melody Siealer, Secret Weapons: Defenses of Insects, Spiders, Scorpions, and Other Many-Legged Creatures (Canada: The Belknap Press of Harvard University Press, 2005) 297-301
8. David L. Wagner, Caterpillars of Eastern North America (Princeton: Princeton University Press, 2005) 79
9. http://entnemdept.ufl.edu/creatures/bfly/tiger_swallowtail.htm downloaded 10-28-18
10. https://en.wikipedia.org/wiki/Papilio_glaucus downloaded 10-21-18
11. https://www.butterfliesandmoths.org/species/Papilio-glaucus downloaded 10-21-18