Eastern Tiger Swallowtail Butterfly

The official butterfly of the state of Delaware, Eastern Tiger Swallowtails (Pterourus glaucus) are named for their tails, which resemble the tails of swallows.

Is the Swallowtail Male or Female?

It’s easy to tell the male Tiger Swallowtail by its pattern of yellow with black stripes.

The females look similar but have a large area of blue on their hind wings.

In areas like Delaware, where the Pipevine Swallowtail is present, a dark form of the female Tiger Swallowtail also occurs, which mimics its poisonous relative.

Tiger Swallowtail caterpillars can eat the leaves of a variety of trees. In Delaware, the tulip poplar (Liriodendron tulipifera) is a favorite. The females also will lay eggs on sweet bay (Magnolia virginiana), wild cherry (Prunus avium), sassafras (Sassafras albidum) and other trees.

The butterfly’s eggs look perfectly round and are laid singly like tiny pearls on the leaves of the host plant.

Small caterpillars resemble bird droppings, a common defense employed by several species. They become green with two “eyespots” as they begin to molt and grow larger, giving them the appearance of a small snake. Like all swallowtails, it also can protrude a gland called the “osmeterium” when threatened.

The caterpillars use their silk to wrap themselves in a leaf during the day.

Prior to pupating, or forming its chrysalis, the Tiger Swallowtail caterpillar turns from green to brown. Also at this stage, like all swallowtail caterpillars, it purges its digestive system, leaving a noticeable pile of watery excrement.

Unlike many other butterfly caterpillars, the swallowtails pupate with their head up, not hanging down in a “J” form. The chrysalis is supported by a silk “girdle.”

The last brood of the season will spend the winter in chrysalis, emerging the following spring when the warmer temperatures signal that there are nectar sources to feed on, and the air is warm enough for their flight muscles to work.