John Metcalfe was CityLab’s Bay Area bureau chief, covering climate change and the science of cities.
The iconic butterflies are having a rough couple years, with declining populations likely due to extreme weather and habitat loss.
In the summer of 2011, a small band of Ontario scientists set out to perform the most ambitious survey ever attempted of the imperiled monarch butterfly. Leading the fieldwork was Tyler Flockhart, a Ph.D. candidate at the University of Guelph, who trekked nearly 22,000 miles through the United States and Canada to bag and tag hundreds of butterflies, which were then put under a lab analysis to determine their birthplaces.
"As far as I know, it's the broadest sample of monarch butterflies through an entire breeding season across North America," Flockhart said recently. The results of the endeavor confirmed what entomologists have fretted about for years: Everyone's favorite butterfly seems to be fluttering on the road toward extinction. "They've been declining steadily," said Flockhart, to the point that 2012 their population numbers in their Mexican winter home were at the lowest point on record.
Tracking these fairylike insects is a dicey proposition because their yearly migration spans vast distances and involves several different generations. The butterflies spend the colder months hunkered in the mountainous fir forests of central Mexico, but in the spring travel northward into America and Canada to be near their larvae's favorite food, the milkweed plant. In the middle of it all are the croplands of the Midwest, where the monarchs engage in a flurry of breeding that sets the direction for future generations to spread over the continent.
The 2013 migration might be the most tattered, disorganized one yet. Researchers in Montreal estimate that the monarch population in eastern Canada is down by about 90 percent, reports CTV News. "The situation right now is dire," one entomologist told the station. Down in Mexico, the butterflies this winter occupied only 2.94 acres of forest – a 59 percent decrease from the 7.14 acres they lived in during the winter of 2011-2012, according to the World Wildlife Fund. The WWF's director for Mexico blamed the decline partly on "[e]xtreme climate fluctuations in the U.S. and Canada" that dry out eggs and kill larvae.
There are other suspected agents behind the monarch's shrinking population. Some people point a finger at herbicides sprayed in American corn and soybean fields, which kill milkweed and limit the places the insects can lay their eggs. Two years ago, a fierce and persistent drought withered up great amounts of milkweed. In fact, milkweed seems locked in a perennial struggle to thrive, due to its status as a nuisance weed deserving of a healthy blast of Roundup.
"People spray it and rip it out, but it's a vital food source for the monarch," says entomologist Marvin Gunderman, adding that sprawl is also to blame for the loss of habitat. "Neighborhoods are expanding, field habitat is being mowed over for more subdivisions, and what's in the open fields? Milkweed."
Despite the rag-tag nature of this year's monarch non-swarm, many folks have reported seeing the black-and-orange critters in their towns and cities. (I saw one myself Friday morning in San Francisco, flying in front of a little girl's face and making her cry. No joke.) Journey North is a wildlife group that collects monarch sightings each year. Here's where people have spotted them this past week:
John Beales, a Montreal-based digital designer, put together this other interesting map of monarch appearances. The "Monarch Butterfly Migration Explorer" uses geotags on Flickr photos to chart where the butterflies are each year. As the crazed cartographers over at Google Maps Mania note, the "difference between the number of monarch butterfly photos taken in 2012 and 2013 looks to be very worrying":
There were fewer photos in 2011, although it was still a more robust year for butterfly photography than 2013:
It should be noted that while these maps suggest that the butterflies are heavily infesting cities, that's just a result of more people living there who are apt to notice them.