Papilio Troilus - Life Cycle

Life Cycle

When female swallowtails decide which leaf to oviposit on, they frequently will drum their forelegs toward a leaf to identify it. Their forelegs have chemoreceptors located in the foretarsi that assess the chemical makeup of the leaf and use that information to decide if it is an acceptable spot. In general, females have shorter and denser sensilla on their forelegs than males, which may be a result of their having to sustain frequent heavy strokes.

The eggs of the Spicebush Swallowtail are greenish-white in color, are fairly large and are laid one or two at a time on a spicebush leaf. Once hatched, the young larvae chew through the leaf from the edge to the midrib, about 3/4 of an inch form the tip of the leaf. The larva lies on the midrib and exudes silk. Upon drying, the silk contracts and causes the leaf to fold up around the larva to form a shelter. At first, young larvae are brownish in color. The brown color of the larvae is independent of leaf color and will occur even on a green leaf. A folded leaf serves as the home for the young larvae. During the day, the larvae remain in the shelter so as to avoid predators and come out at night to feed. Additionally, if larvae are disturbed while rolled up in the leaf, they emit a foul-smelling substance.

When these larvae reach later stages, they turn greenish-yellow before pupating. Older larvae live in a leaf, rolled-up and lined with silk and held together by a line of silk. In order to pupate, the larvae will leave the shelter and find the underside of a leaf near the ground to do so. Upon discovery of a suitable leaf, the larvae begin the pupating process by emitting silk from their salivary glands, which helps attach the larvae to the branch or leaf. Then the larvae turn around while still emitting silk, which creates a "safety harness" for the pupating process. At the end of the pupating process, the larvae have become pupae which are either brown (winter) or green (summer).

The practice of turning either brown in winter or green in summer is called seasonal polyphenism. Because the color of the pupa reflects the color of the deciduous host plants, since the leaves will turn brown in winter and green in summer. Even in cases where the leaves are not yet brown, the pupa appear to turn that color in anticipation of the changing colors.

Roughly three generations of Spicebush Swallowtails occur each year. Most develop into adults throughout the range between the months of February and November. The entire development process from egg to adult takes about a month. Once they have reached the adult stage, Papilio troilus can live anywhere from two days to two weeks dependent on resource availability and predator avoidance.