Over the next few months Vineyarders can be on the lookout for some familiar seasonal residents: the monarch butterflies. The annual odyssey of the monarch butterfly has long delighted scientists and backyard naturalists. In early spring these delicate, diminutive creatures leave their overwintering site in south-central Mexico and make their way north — many traveling upward of 2,500 miles, the females laying eggs as they go. As the season progresses, typically three generations of monarchs, each surviving a month or two, will eat nectar, pollinate flowers and procreate. The fourth generation will live for as long as eight months, some individuals making the entire return trip to back to Mexico over the course of the fall. This is one of the longest migrations on earth, rivaling that of baleen whales. In a constant state of motion, engaged in a transcontinental, intergenerational relay race against the seasons, monarch butterflies are a stunning, colorful embodiment of the earth’s cyclical changes.
Monarch butterflies exhibit remarkable navigational and instinctive abilities, utilizing a circadian clock based in the antennae, the earth’s magnetic field and the angle of the sun to make the grueling journey and find the precise overwintering spots of their ancestors in the mountains of Mexico. Simply following the coast helps too. During the southern migration, many monarchs fly southeast until they reach the Atlantic, then follow the coastline for most of the rest of the trip. That’s partially why coastal communities receive such heavy monarch visitation, especially in the fall. Coastal points like peninsulas and islands can concentrate vast numbers of the butterflies.
Vineyarders are most likely to spot great numbers of migrating and summering monarchs on the southwestern shores of Martha’s Vineyard, especially Aquinnah and Chilmark, since these areas are closest to the mainland. During their fall migration, southbound monarchs tend to be funneled by the shape of the Island, often forming large concentrations near the Gay Head Cliffs in Aquinnah.
On Martha’s Vineyard, monarchs typically arrive around mid-May during northern migration, and numbers peak in late September and early October during their southern migration. Some northbound monarchs choose Martha’s Vineyard as their summer home — although biologists are still unsure how they afford it!
Many theorize that the migration of the monarchs, which cannot survive freezing temperatures and are more of a tropical species, evolved with the northern expansion of milkweed, which is both a vital source of food for the butterflies and the only plant on which they breed. Milkweeds contain milky latex that is poisonous to many organisms. Larval (adolescent) monarchs are resistant to the compounds in the latex and able to ingest large amounts of it. That in turn makes them poisonous or unpalatable to many predators. Adult monarchs no longer feed on leaves but become more generalist eaters, dining on the nectar of a wide variety of flowering plants.
Several species of milkweed are abundant on Martha’s Vineyard, which is another reason why monarchs are common on the Island. Growing milkweed of several varieties, including butterfly milkweed (Asclepias tuberosa), wavyleaf milkweed (A. amplexicaulis) and swamp milkweed (A. incarnata) can be a great way to provide a valuable resource for the butterflies. Several other native Vineyard plants attract nectaring adult monarchs as well, including goldenrods, Indian Hemp, Mottled Joe-Pye-Weed and Common Boneset, as well as various lilacs and asters. Bright-colored flowers are especially attractive to monarch butterflies; the stunning yellow blooms of seaside goldenrod (Solidago virescens) are a particular favorite of southbound monarchs.
Vineyarders, especially those who provide valuable habitat on their properties, may be lucky enough to spot these remarkable travelers in the coming months before they resume their journeys and return to their Mexican havens for the winter.