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What Time is it in Nature: Pipevine Swallowtail

May 31, 2013

The Woolly Pipevine in the Prairie Ridge Nature Neighborhood Garden has been spectacular recently, covered in thick and furry green leaves.  Hidden among the leaves, you will find an insect that depends on pipevines for its survival: the Pipevine Swallowtail butterfly (Battus philenor).  The caterpillars will eventually develop into one of the biggest and showiest butterflies at Prairie Ridge.

Pipevine Swallowtails are, as their name suggests, in the swallowtail family of butterflies.  Like most of their relatives, they are characterized by tails that extend off the back of the hind wings.  Pipevine Swallowtail adults are large butterflies that are deep black with iridescent blue hind wings.  The underside of the hind wings sport seven orange spots in a field of blue, a characteristic that helps distinguish them from other similarly sized black swallowtail species in the area:

pivevine swallowtail adult

Pipevine Swallowtail caterpillars depend on pipevine species as a food plant, so you can often see multiple stages of the butterflies on or around the Woolly Pipevine in the garden.  An adult female flutters around the vine before choosing a suitable place to lay her eggs on a soft, new shoot.  She will then lay 1-25 reddish-brown eggs:

Pipevine swallowtail eggs

After the eggs hatch, the emerging caterpillars feed on the pipevine throughout their larval stage.  When they first emerge, the caterpillars will feed in small groups, but as they age and grow they spread out and eventually feed alone.  While they do change shape and coloration to some extent as they grow, Pipevine Swallowtail caterpillars are generally a deep purple-black or red-brown and develop orange warts along the abdomen with age.  They also have long, fleshy filaments that extend from the sides that grow longer as the caterpillars increase in size:

Pipevine swallowtail larva

When threatened, Pipevine Swallowtail caterpillars use a defense that is common throughout the swallowtails: they evert a sac from their heads (bright yellow in this species) that is covered in a stinky fluid:

Pipevine swallowtail osmeterium

By waving this sac, called an osmeterium, the caterpillars can discourage predators from eating them and gain some protection.

Pipevine Swallowtails are active at Prairie Ridge all summer, so consider making a trip out to see them!  You’re most likely to see adults hovering around the Woolly Pipevine growing to the right of the entrance to the Nature Neighborhood Garden.  Or try looking under leaves with evidence of chewing and you might be able to see a caterpillar lurking in the shade.  They’re well worth a closer look!

What Time is it in Nature is a weekly feature highlighting the current plants, animals, and other wildlife at the Musuem’s public outdoor facility, Prairie Ridge Ecostation. Find out more about the natural happenings at Prairie Ridge at our What Time is it in Nature Archive!

(Photos by Chris Goforth)

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