Waking up in the morning to the sound of red wing black birds is a wonderful sign that spring has finally arrived. Millions of birds are migrating north to nest, breed and spend the growing season in Vermont.
Monarch butterflies are also making their way here, on a journey that is the longest known of any insect migration on earth.While no one really knows for certain why Monarchs travel such a long way, this phenomenon has been happening for thousands of years and is steeped in mystery, spectacle and wonderment.
The Monarch migration story begins in central Mexico, where the North American population from east of the Rocky Mountains overwinters. For several months millions of Monarchs “roost” in high mountain forested locations, completely covering the branches and trunks of oyamel firs, a type of evergreen tree. These forests are part of designated sanctuaries of the Mariposa Monarca Biosphere Reserve.
A population of Monarchs in the western United States winters on the California coast, in areas near Santa Cruz.
The high mountain forests of Mexico are cool and protective, which allows the returning generation of butterflies to stay inactive, so they can maintain a reserve of energy stores all winter. Unlike birds or other animals that make a migratory round trip more than once in their lifetime, the Monarchs that return to Mexico every fall are not the same ones that left in the spring. It is their children’s grandchildren that return the following fall!
In a way is seems like there are two kinds of Monarchs, one being the “summer” butterflies, which are the generations born after they leave Mexico. The last generation—the fourth or fifth, born in late summer—is the population that actually migrates, flying 2 to 3000 miles back to Mexico. However they are biologically and behaviorally different from the summer butterflies.
According to the organization Monarch Watch, “even though these butterflies look like summer adults, they won’t mate or lay eggs until the following spring. Instead, their small bodies prepare for a strenuous flight. Fat, stored in the abdomen, is a critical element of their survival for the winter. This fat not only fuels their flight of one to three thousand miles, but must last until the next spring when they begin the flight back north. As they migrate southwards, Monarchs stop to nectar, and they actually gain weight during the trip! Some researchers think that Monarchs conserve their “fuel” in flight by gliding on air currents as they travel south.”
For many years no one really knew where Monarch butterflies went to for the winter. A zoology professor named Dr. Fred Urquhart and his wife Norah experimented with ways to track butterflies, and eventually perfected a tiny label that could stick to a butterfly’s wing while not damaging it. In 1975, with the help of Monarch Watch, Dr. Urquhart discovered the region of Mexico where the Monarchs overwinter by locating butterflies that had been tagged in the United States.
The Monarchs in Mexico become more active later in March. They mate and begin to fly north, needing to find milkweed plants to lay their eggs on. Timing is very important in this stage of the butterfly’s life cycle; Monarchs are specialized feeders, and only seek plants in the milkweed family. If they cannot find milkweeds to lay their eggs on, then there will not be a next generation of butterflies to continue the life cycle.
Mystery and wonder meet in the interesting relationship Monarchs have with milkweeds. The butterflies gain an important defense against predators by feeding on milkweed as caterpillars. Plants in this family contain toxic steroids known as cardenolides, which are bitter tasting. Through metamorphosis (when a caterpillar “pupates” into a butterfly), the Monarchs store the cardenolides and emerge as butterflies with the steroids still in their bodies. Birds and other animals may try to eat a Monarch caterpillar or butterfly, but will spit it out because they taste so bad.
There seems to be an unanswerable question about the migrating generation of Monarch butterflies: how do they find their overwintering grounds, considering the last generation has never flown to Mexico before? Some sources postulate that Monarchs may use the sun and the earth’s magnetic field for orientation, because their antennae contain a compound that can function like a “chemical” compass.
Although wonders never cease with Monarch butterflies, there are several factors that contributed to a very steep decline in their population, to the point where the butterfly and its magnificent migration may become extinct in the next decade.
Journey North, a partnership that follows the yearly Monarch migration states, “because the monarchs are concentrated in a very small area in the winter, they are more vulnerable during this stage of their life. However, breeding sites in Canada and the US are also crucial to their survival, and additional losses of these sites also pose threats.”
Loss of habitat for Monarch butterflies correlates with the loss of their sole source of food, plants in the milkweed family. Agricultural use of herbicide-resistant crops, and increased use of herbicides to control weeds have reduced milkweed significantly. Monarchs are having great difficulty sustaining their population as they move north in the summer, and south in the fall. Climate change has also been included in some studies as a contributing factor, with rapid weather fluctuations and drought as threats to their survival.
We all can do our part to help protect Monarch butterflies, and our efforts will benefit other pollinators such as bees, moths and birds as well. On the national level, an organization called The Pollinator Partnership is pushing for federal legislation that would encourage more state highway departments to stop mowing roadsides, and plant bee-friendly wildflowers and monarch habitat instead.
You can plant milkweeds in your yard or garden. There are many references to get you started, including an extensive list of plants from Monarch Watch that will attract butterflies and other pollinators. Also check the Ultimate Guide to Butterfly Gardening for many references on how to plan and plant a butterfly garden.
During the month of April, there are two days where you can take action to protect pollinators like the Monarch butterfly. Make Way for Monarchs is introducing a call to action and contemplation for Monarchs and other imperiled pollinators, in remembrance of Rachel Carson, on April 13 and 14. Earth Day is on Tuesday, April 22: set aside time that day to make a difference.