The decline – “a problem with many causes” – is seen in other species, as well, experts say.
Minnesota’s state butterfly is scarce again this summer, a victim of two bad weather years in a row and the decline of caterpillar-sustaining milkweed in the landscape, experts say.
Counts of caterpillars, which transform into monarchs during the summer, are “the lowest we’ve ever seen,” said Karen Oberhauser, a University of Minnesota professor who runs the Monarch Larva Monitoring Project.
But it’s not just a problem in Minnesota.
“I don’t think I’ve ever seen it as low as it is this year,” said Chip Taylor, an ecology and biology professor at the University of Kansas who is also director of Monarch Watch, a research and educational organization, speaking of the monarch population across North America.
Indeed, an estimated 60 million monarchs spent the winter at their customary migration site in Mexico, but 350 million would be customary, said Elizabeth Howard, director of the tracking site Journey North. That’s an 80 percent decline.
Monarch experts said that small coterie laid eggs on its return trip north this year, but the butterflies that hatched across the southern United States in early spring were hammered by drought in the south, then cold weather and lack of food the rest of the way north.
Waconia naturalist Jim Gilbert said he has seen only one monarch so far this year, in his own garden.
He saw none while working in a prairie area near St. Peter on Tuesday. Last year he saw thousands during the northward spring migration, but their offspring were decimated by summer drought before they could travel back south, Gilbert said.
Ordinarily, the distinctive butterflies, with gold-and-black wings trimmed with white specks, are common across the Minnesota landscape this time of year.
Aggressive suppression of milkweed in corn and soybean fields has removed a key piece of the monarch life cycle across much of North America, Oberhauser said.
“There’s a strong correlation between the loss of milkweed habitat and loss of monarch numbers,” she said.
Along with the drought in the second half of 2012, last year’s unusually early spring and this year’s unusually cold and wet one, monarchs are facing “the tragedy of a problem with many causes,” she said.
Other insects down
Vera Krischik, a University of Minnesota entomology professor, added that the absence of monarchs is part of a larger, more disturbing picture. Honeybees, bumblebees, parasitic wasps and many other kinds of beneficial, pollinating insects — including other butterflies — are also noticeably absent this year.
Krischik, who is researching ways to blunt the declines under a grant from the Legislative-Citizen Commission on Minnesota Resources, said linden trees, which are in bloom this time of year, should be buzzing with pollinating insects.
She said she was “stunned” when she checked 30 trees Wednesday and found only a single painted lady butterfly.
“It’s not just that there aren’t monarchs. There’s nothing there,” she said.
Krischik said it’s not just agriculture that has reduced the milkweed and other flowering weedy plants that pollinating insects need for nourishment.
She said it’s also back-yard gardeners with a preference for flowering but sterile, non-seed-producing plants. Butterflies no longer can find as much food in a back yard as they once could, she said.
“We have met the enemy, and he is us,” Krischik said.
However, Howard noted that interest in “butterfly gardens” appears to be increasing, with people planting milkweed and other plants to attract a variety of pollinators.
Taylor’s Monarch Watch has launched a program to encourage people to plant milkweed in their gardens.
Monarch populations have a history of wide fluctuations. A storm in January 2002 killed 80 percent of those overwintering in Mexico, but the population was near normal a little more than a year later.
“But we’re never going to see monarchs like we did, say, in the 1990s,” Taylor said. “We’ve lost too much habitat.”