Despite the recent chilly nights, a few tiger swallowtails were still flittering about our yard on this mild, sunny, autumn afternoon. Members of the genus Papilionidae, swallowtails are represented by forty species in North America and more than 550 across the globe; though their common name reflects a deeply forked tail, not all species harbor that anatomic trait. Birdwing butterflies, the largest members of the genus (and the largest butterflies on Earth), are found in Australia.
After mating, the male swallowtail secretes a sticky substance that plugs the genital tract of the female, ensuring that his genes do not receive competition from another suitor. The female lays her eggs on a host plant (often very specific) and these hatch into caterpillars within a few days. The larvae have several defenses against predation; in their earliest stage, they resemble bird droppings (not terribly appetizing) which molt several times to become large colorful caterpillars with a variety of bright bands and spots (suggesting toxicity). Some species do feed on toxic plants and the ingestion of those larvae can cause sickness or death in some predators; over numerous generations, susceptible predators have "learned" to leave them alone. Finally, swallowtail caterpillars have a gland behind their head, known as the osmeterium, which emits a potent, noxious chemical; while this seems to be effective against other insects and spiders, larger predators (snakes, toads, birds, mammals) are apparently undeterred by its scent.
Among the common North American species are the tiger, black and zebra swallowtails. Tiger swallowtail caterpillars feed on a variety of deciduous trees, black swallowtail larvae (often called parsley worms) feed on members of the carrot family (including parsley, fennel and dill) and zebra swallowtail caterpillars feed almost exclusively on the leaves of pawpaws. Temperate zone swallowtails overwinter as pupae and the beautiful adults spend the warmer months mating and sipping on nectar; depending upon latitude, they produce 2-3 broods each year before cold weather puts an end to their one and only season in the sun.
