When people think of butterflies, they think of summertime. Most readers will probably be surprised, then, to learn that more than 20 butterfly species have been found on the Vineyard earlier than May 1st. Some of these are generalists, migrants or year-round residents that will be with us through the whole season. But a few of them are true early-season specialists, with their entire life cycle and ecology oriented around being active as adults in early spring.
I’ve always had a particular interest in these specialized insects, which push the limits of what cold-blooded animals can tolerate. Most of our characteristic early-season butterflies are small and drab. But some are quite common and easy to find, once you know how to look. They’re associated with some of the Vineyard’s most interesting plants and habitats. And their adaptations to our variable early-season weather are complex and mysterious.
My favorite early-season butterflies are the members of two groups of species, the elfins and the duskywings. The groups are not closely related, but they share two important characteristics: brown coloration and highly specific food plant requirements for their caterpillars. The coloration is easy to explain: before leaf-out, amid the dry litter from last season, a brown butterfly blends right into the background and is hard for a predator to spot. Also, the dark brown color efficiently soaks up the sun’s rays, so these butterflies make the most of whatever heat is available.
The food plant specificity, which seems at first like a liability, is harder to explain. Depending on the species, our four elfins seem to be restricted to blueberry, bearberry, pitch pine, or wild indigo; caterpillars of our earliest duskywing species eat oaks, especially scrub oak. In all cases, the caterpillars prefer (or even require) young leaves or flowers, which are highly nutritious but available mainly at the start of the growing season. In short, these butterflies are committed to precisely coordinating adult emergence and egg-laying with the start of leaf-out in particular plant species: too late in the season, and only low-quality food will be available for caterpillars; too early, and there will be no food at all.
But this strict requirement also offers some important benefits. For a butterfly that does evolve a method of synchronizing with a particular plant species, a food source will invariably be available at the right time. And for butterflies breeding in early spring, caterpillars have a relatively safe environment because many potential predator species are not yet active. The mechanisms that control the emergence of adult butterflies are not well understood. But in the case of these early-season species, the butterflies must have evolved to respond to the same cues, probably based largely on temperature, that prompt their food plants to emerge from dormancy. One hopes that the warming climate and more volatile weather predicted for our future doesn’t disrupt this delicate relationship between plant and insect.
Our elfins – brown, hoary, frosted, and eastern pine – are all, as their name suggests, tiny butterflies, dime-sized or even smaller, and they are fast flyers, making them difficult to spot. Juvenal’s and sleepy duskywings are somewhat larger and readily recognized by their bouncing flight. Open areas featuring their caterpillar food plants are where to look for both groups; in particular, the fire lanes of Correllus State Forest are productive.
These butterflies spend much of their time basking in the sun, often perched on or near the ground. If you’re walking slowly, they’ll flush when you’re about eight feet away, so the key to finding them is to stroll slowly, focusing your attention on the ground in front of you. If you flush a butterfly, follow its rapid, erratic flight, if you can; once it lands, you can study it through binoculars or stalk it, moving slowly and low to the ground. Butterflies are often quite territorial and may circle back to their point of origin. So when you flush one, try standing perfectly still as you follow its flight; it may eventually land fairly close to you.
If you’re experienced at observing wildlife, perhaps as a birder or a hunter, your skills will carry over to butterfly-spotting, to some extent. If you’re a new arrival on the Wild Side, it may take some work to get the hang of spotting an elfin and tracking it in the air . I’d certainly urge any reader of this column to invest the time to develop the knack. While you’re learning, consult the photographs in a field guide (Jeffery Glassberg’s “Butterflies Through Binoculars” is the most popular one) to see what these butterflies look like. Or you can log onto the Massachusetts Butterfly Club’s website, http://www.naba.org/chapters/nabambc, and click on the “Butterfly Photos and Information” tab to view a collection of fine photographs of all the species found in Massachusetts.