If a butterfly flaps its wings in Vermont, will a breeze rustle the needles of an Oyamel fir tree in Mexico? Back in the 1970’s, the Butterfly Effect spun off from the concept of Chaos Theory, which attempted to reconcile the apparent randomness of the universe. The Butterfly Effect holds that the faintest movement of air caused when a butterfly flaps its wings in, say, Vermont, begins a series of interconnected events that may ultimately cause a hurricane in some distant place like Cuernavaca. 

But back to our opening question: The answer is “yes, eventually,” if that butterfly survives the dangerous journey of 2,889 miles from Vermont and completes its autumn migration to the Oyamel fir forests in the Sierra Madre Mountains of Michoacán, Mexico. In the springtime of 2023, monarch butterflies will continue to fulfill their seemingly miraculous life cycle when they begin the journey north.

Populations of monarchs, Vermont’s State Butterfly, are in such marked decline (especially the population in Western North America) that they have recently been designated an endangered species by the IUCN (International Union for Conservation of Nature). Each year they face the multiple threats of declining habitat in their breeding and wintering grounds, pesticides, storms, predators, diseases and parasites. Our warming climate and frequent severe storms are altering the migratory patterns of these minute marvels, who—with an average weight of .5 grams (about 1/6^th of an ounce)—are easily blown off course.

It takes four to five generations of monarchs to complete an annual life cycle. The first generation that flies north in the springtime lays eggs that take five to seven weeks to hatch into another generation that continues the journey north. This pattern recurs, with each generation making its way farther north. The last generation born in late summer survives and flies all the way back to the wintering grounds, where it lives for up to eight months, waiting to migrate north the following springtime. Populations from eastern and midwestern North America overwinter on trees in the Sierra Madre Mountains of Mexico, Honduras and Guatemala.

We now seem to be experiencing a reverse butterfly effect: If climate change heats up the Gulf Stream and contributes to warmer weather, and if it generates a greater number of hurricanes in the Gulf of Mexico, will butterflies stop flapping their wings in parts of New England? The answer is yes, and no.

Elizabeth Crone, Ph.D. and Associate Professor at Tufts University—along with Dr. Greg Breed and Dr. Sharon Stichter—co-authored “Climate-driven Changes in Northeastern US Butterfly Communities,” which was published in Nature Climate Change.

“Climate is getting warmer,” said Crone. “Mobile species move to new areas that suit their climate needs, if there is no other limiting factor. Species from the south are becoming more abundant, and species from the north are less abundant, on average. Many are increasing their range northward, but some species may not be able to move north due to habitat needs and geographic boundaries.”

Shifts in population numbers and geographic ranges have been observed in 100 of the 116 species of butterflies studied. Those species for which climate has demarked the southern extreme of their range are shifting northward, especially in the warmest regions. Those living at higher elevations are more stable, but species found in the lowlands are decreasing rapidly. Research shows that these responses are specifically related to climate.

Frequent hurricanes and severe tropical storms associated with climate change are impacting Monarch butterflies, the only species that migrates long-distance to New England. In recent years, Monarch populations have been about 1/18^th of what they were less than twenty years ago. According to Crone, “Sometime around World War II when pesticides, herbicides and other chemicals became so prevalent, we may have started a shift in butterfly numbers overall.”

Whether or not you ascribe to the Zuni belief that butterflies can predict the weather, they are harbingers of how our environment will evolve in an era of climate change. In Buddhism, butterfly metamorphosis symbolizes the human capacity for transformation—to transcend self-centeredness and be guided by a sense of oneness with all beings. The myriad decisions we make each day will determine the fate of these ephemeral denizens of the air.

Nectar from red clover is one of the monarch butterfly’s favorite late-summer/ early-autumn food sources. Photo: Michael J. Caduto.

What You Can Do 

• Visit the Vermont Center for Ecostudies online “Vermont Butterfly Survey” to report a sighting (https://val.vtecostudies.org/projects/vermont-butterfly-survey/), as well as the popular monarch tracking website, Journey North (https://journeynorth.org/monarchs).
• Make energy-use and lifestyle choices that reduce carbon emissions and slow climate change. 
• Create a butterfly garden of native plants for food and places to lay eggs, such as milkweed for monarchs.
• Don’t use pesticides, herbicides and other chemicals that harm butterflies, bees, and other beneficial insects.
• Maintain open spaces for butterflies to feed, rest and breed. Join Monarch Watch and plant a Monarch Waystation habitat: http://www.monarchwatch.org/waystations/
• Get involved in land conservation to preserve critical areas and prevent butterfly habitat loss. Support conservation groups working toward these ends.
• Inform others about what is happening with butterfly populations and encourage them to track butterflies and work for positive change.