Mid-to-late August is a peak time to spot monarch butterflies in Minnesota. But if you have noticed fewer monarchs fluttering around your back yard in recent years, it is not your imagination.
Minnesota's monarch butterfly population is 38 percent below average this summer, according to preliminary statistics from University of Minnesota's Monarch Lab.
Cool, dry weather is likely the prime culprit, but ecologists also suspect human beings are playing a role.
"If you look at the numbers over time, it would look a little like an EKG, with some high years and some low years," University of Minnesota ecologist Karen Oberhauser said. "We have had more low years recently, which might be a cause for concern."
Oberhauser said agriculture and housing development replace milkweed and wildflowers with crops and lawns. That robs the butterflies of their favorite foods.
The Monarch Larva Monitoring Project tracks butterfly populations with the help of hundreds of volunteers. Every week, the volunteers inspect their milkweed plants and count up all the butterfly eggs and larvae.
It is a methodology that would not work with just any insect.
"Monarchs are probably the only insect that most people recognize to species," Oberhauser said. "Everyone recognizes a mosquito, but there are lots and lots of kinds of mosquitoes, [and] they're not going to recognize the exact species."
From am ecological standpoint, monarchs also serve as a reminder that ecosystems are interconnected, Oberhauser said.
"The adults that we're seeing right now in Minnesota are part of the population that will migrate all the way to Mexico," she said. "So, everything between here and Mexico is important to them. It's symbol of how conservation is a cooperative effort."
Oberhauser said the best thing you can do to help the butterfly population is turn part of your lawn into a butterfly garden. That means planting some flowers and, of course, milkweed.