Wild Side: All hail swallowtails

The most famous butterfly may be the orange-and-black monarch, noted for its size, coloration, and prodigious migration. But the Vineyard hosts three butterflies that are larger and arguably more beautiful than the monarch. All three are widely distributed on the Island, occur throughout the summer, and now is prime time for finding them.

Permanent residents here, and present in above-average numbers this season, are our three swallowtail species: tiger, black, and spicebush. One other swallowtail, the pipevine swallowtail, is a rare visitor that may occasionally establish short-lived breeding population here. Another swallowtail, the giant swallowtail of the southeastern United States, has never been observed here but will be someday: This species, black with a broad band of yellow spots across its wings, is prone to wander, and animals that wander along the East Coast run into the Vineyard sooner or later.

But our regular swallowtails hardly need to be supplemented by imports: all three are striking insects, easy to find, identify, and observe. Most distinctive of the trio, the tiger swallowtail (formally, our species is the eastern tiger swallowtail) richly merits its name, with yellow wings crossed by bold black striping. Essentially a woodland species (its caterpillars probably feed mainly on wild cherry), tiger swallowtails wander widely in search of mates and good nectar sources; like the other swallowtails, this insect will take nectar from flowers both small (thyme or Buddleia) or large (oriental and Asiatic lilies). If you have a garden and have never found a tiger swallowtail visiting, you haven’t been paying close enough attention. The sight of these butterflies half-hovering, half-perching on a flower while probing for nectar is a remarkable one.

Our other two swallowtails are almost as distinctive, hard to confuse with any insect except each other. Both are black with bands of yellow spots on their wings (stronger on black swallowtails, especially males) and iridescent blue areas on their hindwings (most pronounced on spicebush swallowtails, again especially males). It takes a fairly good look to distinguish these species with absolute certainty. But habitat offers a useful clue: spicebush swallowtails are associated with woodlands, while black swallowtails prefer open habitats, including agricultural land (the fields at Katama Farm are the most reliable place to find this butterfly on the Vineyard). With experience, you can distinguish these species consistently just on the basis of wing shape, flight pattern, and size: the spicebush averages larger and longer-winged than the black, and its flight is stronger and more direct.

All of our three swallowtails could occur literally anywhere on the Island; powerful fliers, they range widely, and their distribution is fairly broad to start with. Yet if you look at where the species are most likely, you can clearly see how the ecology of butterflies shapes their distribution. Spicebush swallowtail caterpillars feed on sassafras, a common tree in up-Island woodland. Black swallowtails, on the other hand, use a wide range of plants in the parsley family, including both wildflowers like Queen Anne’s lace and cultivated species like fennel. (In a maneuver quite typical among butterflies, black swallowtails caterpillars have evolved the ability to digest bitter oils in these plants that deter most other insects.)

Because of its association with crop and weed plants, the swallowtail most likely to turn up in your yard, especially if you live in one of the down-Island towns, is unquestionably the black. Like its relatives, the black swallowtail craves nectar from flowers. And if your yard or garden includes a suitable caterpillar food plant for this species, a female black swallowtail is sure to sniff it out eventually.

Swallowtail caterpillars are as striking as the adults. The mature larvae of tiger and spicebush swallowtails, which may exceed two inches in length, develop convincing imitation eyespots behind their heads: Looking like small snakes or lizards, the caterpillars make would-be predators think twice. Black swallowtail caterpillars, when mature, vary somewhat but are typically green with black rings; if you notice chewed parsley or fennel leaves, look closely because one of these caterpillars may be fattening on your herbs!

With all of these butterflies, it’s possible to collect caterpillars, feed them a steady supply of fresh leaves from the plant you found them on, and overwinter them in a cold but sheltered spot until the adults emerge in spring. But if you try this, keep your expectations low: a high percentage of swallowtail larvae fall victim to disease or parasites. Enthusiasts who raise caterpillars stress that the best plan is to collect very young caterpillars, or even the eggs (most easily found by following a female as she lays them). That way, you prevent infection by fungal spores, bacteria, or parasites.

I’ve raised butterflies in the past, and find it satisfying. But you certainly don’t need to make a long-term commitment to appreciate these noble insects. Just watch closely in your yard, your garden, and in woodland clearings where flowers are in bloom.