The State Insect of Arizona: The Two-Tailed Swallowtail
The Big, Beautiful Two-Tailed Swallowtail
This huge butterfly -- the largest in the US -- closely resembles the tiger swallowtail (Pterourus glaucus). The two-tailed is limited to the US west of the Rockies, and even then is more common in the southern portion of that range. It floats like a kite high in the trees along streams and forest edges, coming down to feed at thistles and asters. I remember the first time I saw one, in the Coronado National Forest in Arizona, flying along a stream in the heat of a desert day. It is a truly magnificent insect, and deserves its status as the state insect of Arizona, a state with more than its fair share of cool insects in the first place.
Two-Tailed Swallowtail Showing its "Tails"
The scientific name of the two-tailed swallowtail indicates that it belongs to the genus Papilio, a large group of showy butterflies that often have tails on their wings. Early entomologists thought the tails resembled those of barn swallows, hence the common name. Papilio multicaudata is closely related to the widespread tiger swallowtail, as well as other yellow and black striped Papilio butterflies. It is limited in range to the southwestern United States, but will occasionally stray to central states, where it will typically not breed due to the cold temperatures of the winter months. The southern range of P. multicaudata extends all the way to Central America, where there are many, many Papilio species. Many of these tropical swallowtails are among the biggest and most beautiful butterflies in the world.
Two-tailed Swallowtail Caterpillar
Two-Tailed Swallowtail Caterpillar
The larva of Papilio multicaudata resembles that of the tiger swallowtail, a related species that is widespread throughout the United States. It feeds on chokecherry, ash, and Arizona sycamore, all common trees in much of the state. Most are green, but they turn red or brown before pupating. Note the fake "snake's eyes" on the front sections. Interestingly, the size of the fake eyes is much less important than the shape. In other words, as long as the markings look like eyes, they don't need to be particularly large. Predators will be unlikely to take the chance, no matter how big the "eyes."
Another Swallowtail Species Showing Enormous Fake Eyes
Unusual Features of Swallowtail Caterpillars
Like all Papilio species, the caterpillar of the two-tailed swallowtail has some unique features and behaviors. Most interesting is something called an "osmeterium." It's located right behind the caterpillar's head, and consists of an orange, forked gland that the caterpillar can stick out whenever it feels threatened. The osmeterium looks a lot like a snake's tongue, and is designed to scare off predators like birds and frogs. It also smells bad, a little like rotten fruit. All things considered, it's a pretty great defensive tactic.
Another feature of many swallowtail caterpillars is large false eye-spots near the head. The caterpillar's real eyes are tiny; the big ones are only markings. But combined with the osmeterium, the caterpillar can put on a pretty good "snake show."
Finally, swallowtail caterpillars typically construct a kind of "seat belt" when they pupate. This is a band of silk that supports the chrysalis (pupa) on the stick or twig. No other group of butterflies does this!
The Osmeterium in Action
Yellow and Black: Universal Warning Colors
The bright yellow and black colors of the two-tailed swallowtail are almost certainly a defensive feature designed to warn away predators. Black and yellow, red, or orange are the colors of stinging and otherwise protected insects, a way to advertise to potential predators like birds and amphibians, "stay way! I sting!" Butterflies don't sting, of course, but they may obtain some protection by flashing warning colors to fool a random toad into thinking twice before it tries to make the butterfly its lunch.
Next time you're in Arizona, keep an eye out for this beautiful butterfly!
The following sources were used for this guide: