While I did not pick the headline, and certainly don’t advocate that Monarch butterflies be ignored (any more than any other butterfly species), this op-ed in Sunday’s Baltimore Sun really does reflect how I think our rhetoric about the imminent peril of Monarchs simply can’t be justified by a short and very mixed history of studying Monarch population trends at the macro level.
You can read it with comments and video at http://www.baltimoresun.com/news/opinion/oped/bs-ed-monarch-20160626-story.html
>>Monarch butterflies have become iconic in a way no other insect has. What grade-schooler hasn’t had the obligatory unit on butterfly metamorphosis, illustrated by a zebra-striped caterpillar and robin’s-egg-blue chrysalis and capped with a fast-forward movie of the adult butterfly struggling out, drying its wings and flying away to Mexico for the winter? People who can’t identify any other butterfly know Monarchs on sight.
Their very iconic status, however, has made Monarchs a perfect media darling in the bid by some activists to add the Monarch butterfly to the Endangered Species List and to get the State of Maryland to list it as a “Species of Greatest Conservation Need.” The truth is, Monarchs are not imperiled — in Maryland, in the Midwest, or anywhere in the United States. Monarch butterflies are a very resilient species, capable of population swings of half-a-billion insects or more in a single year.
Best guesses of the population size in Mexico this winter, where the vast majority of Monarchs hibernate in the refrigerator-like conditions of oyamel fir forests, put the number at around 150 million; the highest estimated population number on record was about a billion butterflies in 1997. This 1997 figure is invariably the number that preservationists use to argue for stringent measures to “save” the Monarch “from extinction,” even though it appears to represent an atypical boom year for Monarchs, which — like many insects — show huge variations in number year to year. The long-term average for the past two decades, a mere snapshot in biological terms, is about 300 million Monarchs a year, with cycles three times higher and three times lower.
Some Monarch activists blame these declines on use of powerful herbicides to control weeds in the upper Midwest. Milkweed, which Monarch caterpillars need to survive, is such a weed. And recent declines in Monarch butterflies generally mirror increased use of these herbicides. But more than two decades of counting southbound Monarchs along the East Coast and over the Great Lakes on their way to Mexico shows no significant change in migrant numbers at all even as wintering numbers in the fir forests are swinging like yo-yos. If the numbers of migrating autumn butterflies haven’t changed, clearly herbicides can’t be the culprit. Whatever is happening has to be happening either on the migration journey or in Mexico, not when the caterpillars are munching milkweed.
Moreover, we’ve simply pulled 1997 out of the air (quite literally) to set a notional goal of what a “good” population looks like. Most likely, Monarchs were pretty rare butterflies before large-scale European settlement in North America, because milkweed would have been pretty uncommon, dependent as it is on people or large mammals to bust the sod; milkweed is a creature of exposed soil that happens rather seldom in nature. Farmers who plowed the Great Plains probably sent milkweed — and Monarchs — into a population explosion the likes of which North America had never seen before and that continued (and possible still continues, relative to pre-European numbers) through the post-colonial times.
Here in Maryland, where the Monarch population is robust, the butterflies can been seen throughout the summer months in small numbers and in large flights off the coast in their autumn migration. We’ve never had huge numbers of summer Monarchs here; it’s against their biological nature, which is to lay eggs in early summer on such milkweed as they can find in the mid-Atlantic (more than enough to support their population in the East, it would seem), grow, mature, and fly farther north for a second and even third generation in the Northeast and Canada. In late summer and early fall practically local every field or garden can boast transient Monarchs.
If Maryland retains Monarchs as a species in need of extreme conservation measures, or the U.S. adds Monarchs to the Endangered Species List, Monarch butterflies will be the only such species that any Maryland citizen can stand on a beach in September and see by the hundreds or thousands, making a mockery of laws designed to safeguard truly imperiled species and eroding public understanding of what it means to be an endangered species in need of state or federal help to survive.
Rick Borchelt is a science writer who lives and blogs about natural history in College Park. He is moderator of the local butterfly observation and research site, leplog.wordpress.com.