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Mar 18, 2019 3:08 PMPublication: The East Hampton Press & The Southampton Press

Surprise Housemate: Black Swallowtail

This male black swallowtail butterfly emerged last week from its chrysalis, which was on a geranium plant taken indoors for the winter.  DEBORAH WICK DEBORAH WICK
Mar 18, 2019 3:08 PM

It seemed as if spring had sprung this past week. As I mentioned in a previous column, signs of spring are most notable among the animal kingdom, while our landscape retains its winter look.Osprey are back. Four common loons and a small fleet of red-breasted mergansers worked a large school of baitfish from below in Accabonac Harbor last Thursday, while several dozen gulls attacked from above. It must have been a thick school, as the gulls never failed to regain flight without a small fish in their beaks. Unfortunately, I could not determine the ID of the 3-to-4-inch-long, slim, silvery prey.

Red-winged blackbirds are making music in our swamps by day, and the spring peeper chorus takes over at night. Turtles are out basking in the sun. Northern cardinals have been around all winter, but I heard my first male singing over the weekend, staking out its nesting turf.

Bob and Deborah Wick of Amagansett reported the most unusual sighting of the week. They had brought their potted geraniums inside for the winter and, unbeknownst to them, attached to one of the plants was the chrysalis, or cocoon, of a black swallowtail butterfly (Papillio polyxenes). On Saturday, March 9, they noticed the striking adult, slightly smaller in size than a monarch butterfly, fluttering about the house.

Black swallowtails have two generations per year here on Long Island. According to data collected by the NYC Butterfly Club and presented in Jeffrey Glassberg’s excellent book, “Butterflies Through Binoculars: A Field and Finding Guide to Butterflies in the Boston–New York–Washington Region,” the last generation metamorphoses into winged adults in late August through mid-September, and a few adults can be seen flying about in search of a mate as late as early October.

My references state that the average lifespan of the adults is 10 to12 days, although there are records of some living up to 40 days. Males and females can be distinguished by the size of the two rows of yellow spots on the back edge of the upper wings (larger on the males) and the amount of blue on the upper hindwings (more on the female). Both have the distinctive red and black spot on the hindwing.

The female’s color pattern mimics that of the pipevine swallowtail butterfly, the latter being poisonous to protect it from predators. While the male and female black swallowtail are easily distinguished from above with their wings open, their color pattern on the undersides of their wings is the same, and the male enjoys the mimic strategy by keeping its wings upright at rest such that only its pipevine-like undersides are exposed.

Black swallowtails are found in open fields, meadows and tidal marshes, and are well adapted to suburban landscapes where they find nectar sources among the clover flowers in lawns, and in backyard gardens among a wide variety of flowering plants including zinnia, sunflower, lilac, purple coneflower, milkweeds and thistle. I’ve noticed black swallowtails nectaring on my buddleia plants, aptly named “butterfly bush.” They are even found in urban environments. Their eggs have been found among parsley plants growing on New York City high-rise terraces.

After mating, the female lays spherical, yellow eggs on host plants in the carrot family (Apiaceae), generally one per plant, 35 to 50 eggs per day over the course of 10 days, for a total of 200 to 430 eggs per female. Other host plants include parsley, dill, fennel, Queen Anne’s lace, wild parsnip and celery. The egg stage averages four to nine days. Newly hatched larvae are black with a white “saddle” at the mid-point of their topsides. This mimics a bird dropping. They are tiny and difficult to spot at first.

This caterpillar or larval stage lasts 10 to 30 days during which it goes through five “instars” or molts, eventually reaching 2 inches in length and somewhat resembling a monarch caterpillar at first glance, with a green body and black, yellow and white bands and spots. They also develop bright yellow-orange, retractable, horn-like structures behind the head. Called the osmeterium, this defense organ is extruded when the larvae is threatened, and emits a repellent that is particularly effective against ant predators.

When fully-grown and ready to pupate, the caterpillars leave their host plants and can travel some distance to find a suitable location to adhere to a branch with silk, shed its skin, and transform into a chrysalis. The first generation chrysalis forms in summer and is usually green to best camouflage among the leafy plants. This stage lasts 9 to 18 days. The second generation chrysalis forms in fall and is usually brown, as it will last through the autumn leaf drop, through the winter, and into spring, with the winged adults emerging as early as late April but more commonly in late May.

The Wick’s male black swallowtail, having been moved indoors for the winter during its pupal stage, was tricked into emerging nearly two months early when there were no flowering plants available to nectar at. A solution of sugar water was placed in cones and saucers in the hopes of keeping the new housemate alive, but it did not seem interested. Bob described the situation thus: “Deb made a little ‘flower’ with sugar-water solution inside. He didn’t take to it but instead has taken up very still residence attached to a beautiful pillow, all despondent about his ill-timed metamorphosis, not eating, and alas no sex for him. Not sure which he is more despondent about.”

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