Tiger Swallowtail

Recently a Tiger Swallowtail butterfly fluttered into a store. Someone said, "It's a moth! It's going to eat the fabric!" Someone else said, "It's a Monarch butterfly!" 

"It's a Tiger Swallowtail butterfly," I said, but my quiet reasonable voice was lost in the commotion as people were chasing the butterfly, dodging it, or dodging those chasing it.

Clearly there is a need for a post about the Tiger Swallowtail butterfly, a human-friendly creature on the whole, though not one I'd choose to handle (as someone in the store eventually did).

Though sometimes nicknamed "monarchs of the woods" and suchlike, Tiger Swallowtails are a completely different species from the one called Monarch butterflies.

Photo courtesy of By HaarFager at English Wikipedia, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=5373024

Actually, Tiger Swallowtails are a group of species. They are found in almost every part of North America, different species in different regions. Slight but consistent differences show experts whether a butterfly found where species ranges overlap is Eastern, Western, Canadian, Appalachian, etc. In my part of the world, I always thought the slightly paler yellow ones might be individuals who'd grown up in different conditions than the brighter ones, but scientists now say the pale ones are Appalachian and the brighter ones are Eastern. 

Anyway, note that the Tiger Swallowtail is yellow (some females are black; more about this later) and its most conspicuous black stripes cross the veins in its wings. The Monarch, shown below, is orange (some individuals are white; more about this at monarch-butterfly.com) and its black stripes outline the veins in its wings.

Photo courtesy of By Kenneth Dwain Harrelson, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=14917505

Which is bigger? Individuals vary; these two species are the biggest butterflies normally found in Virginia. Monarchs' wingspread tends to be wider. Tiger Swallowtails' wings are longer, especially when spread out in museum displays. Both butterflies are very large and showy...in contrast to the moths that eat fabric (in their larval stage). The Clothes Moth is so small that, although some individuals have interesting patterns of black and white spots on their drab gray wings, humans seldom notice. Clothes Moths usually fold their wings in over their backs, anyway.

Eastern Tiger Swallowtails are wider and longer than the palm of most people's hands. At times males are even aggressive, to the extent that aggressive behavior is possible for butterflies. Butterflies “fight” by flapping through each other’s space, which can create drafts and knock the other butterfly off course, and Tiger Swallowtails frequently fly head-on toward larger animals, or even cars. They also frequently mistime their threat-display flight toward oncoming cars, and are found beside paved roads, stunned or killed.

Tiger Swallowtails have distinct sex roles and fairly distinct sex-linked color patterns. Males are yellow and black. Some females are yellow and iridescent blue-black, in a pattern similar to the males'. Other females are predominantly iridescent blue-black, with spots on the hind wings similar to the yellow females'. In the 1980s an amusing study reported that dark females have a better survival rate due to their resemblance to other Swallowtail butterflies that are toxic when eaten, but yellow females have a better reproductive rate due to males being more likely to approach them--proving that Anita Loos' "Gentlemen prefer blondes, but gentlemen marry brunettes" is truly biologically based, right? Other studies did not find this tendency to be consistent. 

Baby Tiger Swallowtails eat new, young leaves at the tops of trees. They can live on several kinds of leaves but they thrive and multiply most conspicuously where there are a lot of tulip poplar trees. In Virginia, after the logging boom a hundred years ago, the first tall trees to re-form our forests were tulip poplars; thus we used to see hundreds of Tiger Swallowtails at every puddle, engaged in social behavior known as lekking and biological behavior known as composting. As slower-growing trees replace aging and dying tulip poplars, we're seeing fewer Tiger Swallowtails. They are still our official state butterfly.

In addition to chasing cars and (sometimes) choosing mates who are less likely to survive (probably by flying toward another yellow butterfly in an aggressive display, then realizing at close range that it's female), male Tiger Swallowtails also seek out and eagerly slurp up all the nastiest messes on the ground. They like oil spills, dung, and carrion. From these sources they extract mineral salts, which their bodies need to digest. Females usually slurp up flower nectar; they absorb and digest mineral salts through contact with males. 

Observing the behavior of creatures like the male Tiger Swallowtail has led scientists to question exactly how much these creatures have in the way of brains. The Tiger Swallowtail has very few neurological structures corresponding to the brain in other animals. What sense, or senses, a butterfly has are distributed around its body in ways that seem bizarre to humans. Butterflies slurp up liquid nourishment with their long tubular tongues, but they “taste” things, before slurping, with their feet. So it is not unusual for a Tiger Swallowtail to fly at a human, land on an arm or leg or even the face, decide the human’s sweat tastes good, and linger to remove a few mouthfuls of sweat from the human’s skin. This is the butterfly most likely to perch on your hand, or even walk up and down your arm, for several minutes. Males do this more often than females, but despite their aggressive defense of what they’ve defined as their mating territory, Tiger Swallowtails share nourishment with other butterflies of any sex or species...so if you hold still long enough, it’s possible to induce two or more Tiger Swallowtails to share your sweat. But, in view of the other things they taste and like, why would you want to? 

Tiger Swallowtail caterpillars are easy to see on the ground, but are almost never found on the ground. If they can, they spend their caterpillar days in the treetops. Their main defense against birds is being the same shade of green as a poplar leaf, which makes them a little harder to see, but if they survive into their fifth caterpillar skin (the “final instar”) they acquire a funny little forked “tongue” they can stick out, located across where their shoulders would be, if they had shoulders. The “tongue,” or “osmeterium,” resembles a snake’s tongue and has an odor that birds seem to dislike. (The individual below is not sticking out its osmeterium.)

Photo courtesy of Jerry F. Butler of the University of Florida. This picture, and several other nice clear pictures of Papilio glaucus, are at https://entnemdept.ufl.edu/creatures/bfly/tiger_swallowtail.htm .

Monarch butterfly caterpillars look completely different. In nature you would never find a caterpillar at each stage of their development all in a group on one leaf. People rear monarch butterflies in cages, making it possible to pose these caterpillars together, showing how fast they grow. They develop from the tiny stage 1 to the comparatively huge stage 5, as shown below, in about a month.

.Photo courtesy of Ba Rea at https://blog.nwf.org/2014/09/a-visual-journey-through-the-monarch-life-cycle/ .

In temperate regions "large caterpillars" usually grow to about two inches long. Tiger Swallowtails and Monarchs are bigger butterflies, and some individual caterpillars can be three inches long. What these completely different-looking caterpillars have in common, other than size, is that they don't live in cozy family groups, as some other moth and butterfly caterpillars do. In a dim way bigger, older Eastern Tent Caterpillars seem protective of their little brothers and sisters. Monarch and Swallowtail caterpillars are not. They are shell eaters; they eat their own cast-off skin. A natural appetite for their own skin leads them to eat other skins of their own kind of caterpillars too, and too bad about the sibling who might have been still occupying that skin. It would be cruel to leave a collection of caterpillars, like the baby Monarchs above, together for longer than it took to snap their picture. In nature these caterpillars hatch from eggs placed far enough apart that two caterpillars never meet, so they have no social instincts whatsoever. They probably don't have enough brain to realize that their instincts lead to cannibalism, but it happens. 

While turning into butterflies these species look even more different. Monarch pupae hang from a thread and look like little green leaves. Tiger Swallowtail pupae are braced at an angle to tree branches and look like broken twigs. 

As butterflies, they behave differently. Monarchs are seen as having "royal" qualities because they like a lot of space. Though they fly longer, while carrying more weight, than our other butterflies do, they fly at a slow, almost languid pace. In a quiet garden you can hear their wings flap. During the breeding season, after the mass migrations, Monarchs spread themselves out and avoid places where other Monarchs are or have been. This is not because they have any cannibalistic or hostile impulses; the adult butterflies eat only flower nectar. Rather, each female looks for a fresh, untouched milkweed plant on which to lay each of several hundred eggs, and males tend to follow females. Occasionally you might see two Monarchs apparently fighting, not only flying close enough to disturb each other's air but flying into headlong collisions. This is play-fighting. The pair are courting. They don't hurt each other as they fall to the ground. They may mate, or part as friends. You are likely to see only one Monarch in spring and one in fall, because other Monarchs can smell that one has already visited your neighborhood and will look for other places to migrate through. 

Named for their stripes, Tiger Swallowtails aren't predators. They are a composter species. However, they gather around puddles and nasty stuff, where the males slurp up those mineral salts in clusters, sometimes of dozens or hundreds, and females hang around the edges and check our the males. These gathering sites are called leks; the pattern of behavior is called lekking. In the case of butterflies, "licks" would also be appropriate. As they satisfy their appetites and leave the leks, males are likely to flit off with one of the female spectators. They travel several hundred yards together, sometimes play-fighting and teasing, and ultimately mate. Though some smaller, shorter-lived moths and butterflies mate only once, butterflies don't seem to form pair bonds. Females flit off to lay their eggs. 

Like Monarchs, Tiger Swallowtails look for a different tree branch for each egg. Because they can use big trees rather than flower plants, however, Tiger Swallowtails don't need to fly as far as Monarchs do. In places that have four distinct seasons, all butterflies show some vestigial pattern of seasonal migration, though no other species migrates as dramatically as Monarchs do. Individual Tiger Swallowtails may linger at the same place for several days. If the females find enough suitable tree limbs and all of them find enough edible liquids, individuals may not travel far, nor will they necessarily migrate northward in spring and southward in autumn. Maps of the whole species population would, however, show movement northward in spring and southward in autumn, as their food plants grow.