By RICK BORCHELT
From October until the first frosts, a river of orange flows through Maryland — a river of monarch butterflies, that is, that begins as a trickle in Canada’s Maritime Provinces and ends as a torrent that inundates whole mountain forests in Mexico.
For most of this month, monarchs (Danaus plexippus) in the eastern U. S. will use Maryland’s beaches, meadows, marshes and gardens as stopovers where they replenish their energy to fuel a migration that can be several thousand miles long. Nectar is their fuel of choice, and they need copious amounts to make it to their wintering grounds.
Not that long ago, most eastern monarchs migrated south right along the Atlantic coast, taking advantage of the near-constant sea breeze to coast, not flap, conserving energy until they cleared the tip of the Appalachians and made a sharp westward turn, on course for Mexico. Along the way, they would refuel with nectar from once-abundant seaside goldenrod, a flower specially adapted to life on the coast. Indeed, dunes from Cape Cod to Cape Canaveral were once carpeted with gold.
Today, however, most of those coastal dunes have been transformed into seaside developments that have pushed the monarch’s migration route inland to find nectar, away from the coast. The consequences of this westward shift are dramatic: Without sea breezes, monarchs have to flap more than glide, and they lose energy with each flap. Seaside goldenrod is scarcer now, and the plants that remain are patchily distributed, so the much-needed nectar is harder for monarchs to find. Fewer and fewer monarchs have the stamina to reach their southern overwintering sites.
Much has been written in the past two or three decades about whether monarchs are in imminent peril of extinction in North America. It’s helpful to keep in mind that monarchs really represent three distinct populations in the United States: our eastern butterflies, a midwestern population that overspreads the Great Plains and prairies into Canada, and a small western cohort that moves up into the mountain meadows of the Rockies in the summer and winters in eucalyptus groves along the Pacific. Eastern populations seem to be doing the best; the annual count passing through a long-standing monarch watch location in Cape May, New Jersey, has been relatively steady for decades.
We’re also just learning that not all monarchs end up in Mexico, either, where observers perform the most precise annual monarch census. Scientists in recent years have discovered that at least a few of our local migrants don’t take that turn west but keep heading south to Florida, from where they stage their spring comeback when the weather warms up. Just this past year, researchers also discovered a previously unknown overwintering population of monarchs in the coastal swamps of South Carolina.
Even with these variations on their migration theme, it’s true that monarch butterflies are probably much less common than they were just 75 years ago — and in some places, dramatically so. Some organizations have even called for monarchs to be listed as an endangered species.
Paradoxically, though, they are still probably much more common than they were when Europeans colonized North America.
The fortunes of monarchs are inextricably tied to the fortunes of milkweed, a widespread genus of wildflowers (Asclepias) found across the United States and the sole food source for monarch caterpillars. The most common milkweeds are considered early succession plants, plants that have adapted to and thrive in continuously disturbed soils. European settlers, many if not most of whom were farmers, and the sodbusters of the 1800s created sizable tracts of such soil. More recently, Big Ag has created even broader expanses of tilled soil for crop monocultures. Once forests or prairies reassert themselves, though, milkweed dies out quickly.
Paleopalynologists — researchers who study ancient pollen — have traced two distinct milkweed population booms over the past 25,000 years, first when the great ice sheets of the Pleistocene retreated about 12,000 years ago and left behind bare ground, and again beginning about 250 years ago when large-scale conversion of forest to agriculture began in the U.S. Both transitions opened up vast acreages where milkweed, which had likely been uncommon, could grow. Monarchs would have been uncommon too — much less common than they are now.
There is no question that monarch populations today are under stress from severe weather exacerbated by climate change, human activities that alter their habitat, and widespread use of herbicides and pesticides.
The standard solution offered by many conservation groups is to plant more milkweed, and that may help the midwestern monarchs. In Maryland,, however, and in much of the eastern United States, there is more than enough milkweed. It’s so abundant, in fact, that much of it goes unused during the summer by the small butterfly population that remains in the Mid-Atlantic. Like many of us, most monarchs continue northward for the summer where it is cooler, and there are fewer diseases and predators, returning to Maryland only on their southward sojourn.
It’s never a bad idea to plant milkweed, which supports a lot of other native pollinators, too. But Marylanders can help monarchs most by planting nectar-rich, late fall flowers, especially native ones like asters, goldenrods, bonesets and ironweeds. While we won’t see spectacular mass migrations of monarchs here, we’ll see our own branches of the river of orange flowing through our backyards.