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Thursday, July 11, 2013

Tails of Summer

Giant Swallowtail, Papilio cresphontes

Flower blooms in summer are often visited by large, colorful butterflies in the swallowtail family. These insects are so named because of the tails on their hindwings that resemble the forked tails often found on birds in the swallow family.  They are even more unique when in the caterpillar stage, because they possess a hidden structure behind their heads called an ‘osmeterium’, a fork-shaped organ that is exposed when under threat (or forced out with a gentle squeeze) and can emit a smelly and bad-tasting secretion.  As such, swallowtails are distasteful to many predators in both the caterpillar and adult butterfly forms.

The smallest and darkest swallowtail you will see this time of year is the Pipevine Swallowtail (Battus philenor).  Its upperside has blackish-brown forewings and hindwings that have an iridescent metallic blue sheen.  The undersides of their hindwings have bright orange dots surrounded by black and blue, with subtle white markings.  The Pipevine Swallowtail caterpillars, which are reddish-brown with rows of fleshy red tubercles rising up from their backs, normally feed in small groups on plants in the pipevine family.  It is these plants that give the insect their poisonous quality.
Pipevine Swallowtail caterpillar
Pipevine Swallowtail chrysalis
Pipevine Swallowtail, Battus philenor

One of our bigger and brighter swallowtails is the Two-tailed Swallowtail (Papilio multicaudata). Growing to over 5 inches wide, their distinctive yellow wings have black tiger-like striping, with a row of bright blue spots along the trailing edge on both sides of the hindwings.  Each hindwing also has two primary black tails, giving this insect its common name.  The Two-tailed Swallowtail caterpillars are carrot-orange with a pair of pale yellow eyespots on top of the head and a pale yellow band behind the head, making them resemble a small snake.  In our area, these caterpillars feed on the leaves of the wafer ash or hop tree.

Two-tailed Swallowtail, Papilio multicaudata
Our largest butterfly is also a swallowtail, is aptly named the Giant Swallowtail (Papilio cresphontes), and can often have a wingspan of over 6 inches.  Their wings are dark brown to black with yellow bands and a yellow spot in the center of each tail on the hindwings.  Their young caterpillars look like bird droppings, which are effective at deterring predators.  Giant Swallowtails have distinctive flight patterns, with the females tending to beat their wings slowly but move quickly over long distances, and the males having a more rapid, jerky flight due to their slightly smaller wings.

Giant Swallowtail, Papilio cresphontes
At times you may find an adult swallowtail butterfly missing some or all of its tails.  While the true purpose of the tail-like extension on the hindwings of these butterflies is unknown, it is often believed that they trick predatory birds into biting off this expendable part of their wing, giving the swallowtail a chance to fly yet another day!