Nearly all Prince William County residents have likely noticed the Eastern Tiger Swallowtail, one of the most common butterflies in our area and Virginia's state insect.  At wingspans of up to 6 1/2 inches, it is also one of our largest butterflies.

The Eastern Tiger Swallowtail inhabits deciduous woodlands and their borders, which includes many of our parks and residential neighborhoods.   

What many of us may not have noticed, however, is how to tell a male Tiger Swallowtail from a female.  The key is in the color blue:  though both males and (some) females have the black "tiger" stripes on their forewings that give this species its nickname, females have a much greater proportion of blue coloring on their hindwings. 

In addition, female Tiger Swallowtails actually occur in two very different color schemes, or "morphs."  The yellow morph looks much like the male, but with more blue on the hindwings; the dark morph is nearly entirely black or dark gray, with yellow spots on the rear edges of the wings and prominent blue on the hindwings. 

The female dark morph is sometimes confused with the Spicebush Swallowtail, but can be distinguished by the absence of a second band of orange spots on the underside of the hingwing. Also note a wavy black band that divides the blue areas on the hindwings of the Tiger Swallowtail, as well as the fact that the Spicebush Swallowtail's wingspots are more green than yellow, as in the Tiger Swallowtail.

Adult Tiger Swallowtails feed on flower nectar from many wild native plants and garden species, including milkweeds, thistles, coneflower, Ironweed, and Red Clover.

Females lay their green eggs singly in the leaves of woody plants that the caterpillars can eat. Tiger Swallowtail Caterpillar feed on the leaves of a variety of woody plants, mainly tulip trees (Liriodendron tulipifera) and wild black cherry (Prunus serotina).   

In its earlier stages (or instars), the Tiger Swallowtail caterpillar is dark brown and white, camouflage that makes it resemble a bird dropping.  In later instars, it changes its "costume" to become bright green with a swollen thorax and a band of faint blue dots on each abdominal segment, as well as black-and-yellow false eyespots. 

Though it no longer has its protective camouflage, it turns to theatrical tricks to discourage predators, rearing its head in an aggressive pose, said to resemble the Hognose snake.  If that isn't enough, the caterpillar continues its act, extending its osmeterium, a fleshy organ with two red horns that resembles a snake's forked tongue, and emits a foul-smelling secretion.