It began with an article in the March/April 2014 issue of The American Gardener, “Plight of the Butterfly” by Gabriel Popkin. I knew that monarch butterfly populations in their Mexican overwintering forests had decreased in recent years, but this article provided the statistics: last winter’s monarch overwintering area was the lowest ever recorded, 1.65 forest acres compared to a peak of 45 acres in the mid-1990s.The number of monarch butterflies summering in Maine has also declined. Ann Judd, Master Gardener Volunteer and leader of the monarch project at Charlotte Rhodes Butterfly Garden in Southwest Harbor, Maine, reported all time lows in monarchs spotted at a nearby field of common milkweed: only two monarchs were seen in this field in the summer of 2013.
Causes of this drastic decline include winter habitat loss to timber cutting in Mexico and several consecutive spring droughts that desiccated monarch eggs, reducing the number that hatched. But most scientists agree that the number one cause is reduction in milkweed populations along the monarch’s migration routes due to the use of herbicides on fields of herbicide-resistant corn and soybean varieties. All other plants are killed, including nearby milkweed. This ecologically-destructive farming strategy is lethal to monarchs, as milkweeds are the only plants that monarch caterpillars will eat; without them, the species cannot complete its life cycle.I asked Ann Judd which species of milkweed she recommends to New England gardeners who want to help restore summer monarch populations in New England. She suggested planting Asclepias syriaca, common milkweed, in open fields or other areas where its rhizomatous habit can be tolerated. It is the best perennial species from the monarch’s point of view but too aggressive for the home garden. Another perennial species, A. incarnata, the swamp milkweed, works well in the perennial border where it will be a magnet for butterflies and other pollinators.
“Even a tub of the South American species A. curassavica, tropical milkweed, a continuous bloomer, can get a family interested in the monarch cycle if they don’t have a back yard for a garden,” said Ann. “My goal is to have schools and senior centers, libraries, golf courses – everyone really, getting something started. It would make a difference in any community if everyone tried.”
In early March there were only a handful of young swamp milkweed plants in Marjorie’s Garden, too small to attract passing monarchs, so I purchased several packets of tropical milkweed seeds, germinated them indoors and, in early June, transplanted about three dozen seedlings in the garden. Most went into two small beds in the vegetable garden, and a dozen were planted in a large “whiskey barrel” tub at the porch steps. We waited to see if any monarchs would find us.
Grow It and They Will Come
Our milkweeds, both the perennial and the tropical annual, grew slowly through the spring, but as the days lengthened and temperatures rose, the annuals burst into bloom. By the end of June each plant bore several clusters of orange-red flower buds that soon opened to reveal deep yellow petals.
On a warm early-July morning, while working in the garden, I caught a glimpse of a monarch soaring over the deer fence and into the vegetable garden – the first monarch butterfly to ever visit Marjorie’s Garden, as far as I know. It flitted about for a few minutes and then disappeared. That afternoon there were two monarchs flying about the garden. I kept watch as I worked, hoping to see them come to rest on the tropical milkweeds, but I saw no monarchs touch down in Marjorie’s Garden.
Yet monarchs did touch down, for on July 20 there were small monarch caterpillars on all the tropical milkweeds. Slender and hard to find at first, they grew rapidly as leaf area on the milkweed plants grew smaller. By the first of August we counted 24 fat caterpillars nearing the end of their two-week larval stage, almost ready to pupate.When monarch caterpillars pupate, they leave the milkweed plants and disperse. Before this could happen, we transferred nine caterpillars to hatching cages for tagging (see below). Of the remaining 15, we easily discovered six chrysalises attached to plastic strands of the deer fence. The rest of the pupating larvae were hidden in the garden.
In the hatching cages, each caterpillar continued to feed on cuttings of milkweed for a while before crawling up the mesh side of its cage to the top where it attached itself upside-down to the plastic roof, assuming the shape of a “J”. While what followed can all be explained as chemistry, it has the aura of lepidopteran magic. The caterpillar at dusk transformed into a translucent lime green chrysalis by dawn, the contents of the chrysalis little more than a bag of fluid.
Keeping WatchDaily checks over the next two weeks showed little change in the chrysalises. They were buffeted by winds, pounded by rain, and baked by the sun, but otherwise remained the same color and size. As the time approached for the emergence of adult butterflies from these tiny capsules, we could see the orange and black markings of wings through the thin shell of the chrysalises.
And then, about 24 hours before emergence, the color of each chrysalis changed to a dark grey-green, almost black in poor light. Often this color change occurred late in the day and by dawn the adult had emerged. We would find it clinging to the transparent shell of its chrysalis, to a nearby stem, or to the mesh walls of the hatching cage, pumping its wings to fill them with fluid.Making my rounds of known chrysalis locations, I came across a chrysalis from which the adult was just emerging, its wings crinkled like tissue paper around its swollen abdomen. Over a thirty minute period, the wings slowly expanded until they appeared nearly full size, but still very fragile, easily creased as the butterfly slowly crawled about the empty chrysalis shell. It would be several hours before the monarch could fly.
Each day brought more monarch butterflies in the air above Marjorie’s Garden. They sipped nectar from summersweet clethra, purple coneflowers, mexican sunflowers, zinnias, and, of course, tropical milkweed. They soared over the deer fence into the vegetable garden. They floated gently into the high canopy of a birch tree, their orange and black markings distinctive among the dark green leaves.
Monarch Watch, a nonprofit education, conservation, and research program based at the University of Kansas, runs a monarch tagging program to keep track of monarch numbers and to track any shifts in the origins of monarchs that reach Mexico. Ann Judd manages the Monarch Watch tagging project at Charlotte Rhoades Butterfly Garden, a program that involves transferring mature caterpillars from the garden to hatching cages for pupation. At the end of the two-week pupation period, on the day after the adult butterfly emerges from its chrysalis, it is carefully removed from the cage and the center of one wing tagged with a small paper disk. A number on the tag identifies the butterfly’s tagging location and sex. If recovered, the tag provides information on mortality during migration. Since the total number of butterflies tagged each year roughly parallels the numbers overwintering in Mexico, tagging also provides a benchmark of shifts in the number of migrating monarchs.Of the nine caterpillars that we placed in hatching cages, eight adults were successfully tagged over a three-day span (one never emerged from its chrysalis). As I gently grasped the folded wings of each butterfly, Marjorie applied the tiny paper disc to the outer wing. We then released the monarch on a cluster of tropical milkweed to begin nectaring.
The two monarch butterflies that flew into Marjorie’s Garden in early July were third generation descendants of butterflies that spent last winter in Mexico. In some mysterious way they found the small patches of milkweed plants growing in our little garden, deposited eggs on the leaves of those plants, and moved on. By the time you read this, the adult monarchs raised in our garden will be winging south, to the oyamel fir forests of Mexico, to begin the cycle anew.
In all of this there is this truth: two gardeners tending a small garden can make a difference. Imagine a world in which every garden has a patch of milkweed.