Mowing milkweed fields helps monarch butterflies

"This could eventually lead to management recommendations to transportation departments in Michigan, and other midwestern states," researcher Nate Haan said.

By Brooks Hays

March 12 (UPI) -- Monarch butterflies face a number of threats, but lawnmowers aren't one of them. According to a new study, freshly mowed fields can actually benefit monarch butterflies.

According to a new study, published this week in the journal Biological Conservation, monarchs lay more eggs on young milkweed. During their larval stage, butterflies only eat milkweed.


"Monarch butterflies scout young milkweed to lay their eggs," Nate Haan, postdoctoral research associate in entomology at Michigan State University, said in a news release. "And in terms of a food source, milkweed is more like spinach when it's young and comparable to cardboard as it ages."

Because fewer predators visit milkweed when its young and without flowers, the butterflies are more likely to survive their larval stage.

Monarch butterfly numbers have been steadily dwindling over the last 20 years. Scientists blame their decline on deforestation near their wintering grounds in Mexico, as well as pesticide exposure and habitat loss along their migratory routes through the United States.

"The habitat for monarchs is shrinking; it used to include corn and soybean fields but now it's restricted in many places to pastures, parks and right of ways along highways and interstates," Haan said.


Haan and other scientists at Michigan State have been working the Michigan Department of Transportation, as well as a variety of public land managers and private landowners, to develop new monarch conservation strategies.

Experiments with mowing patterns showed monarch butterflies laid more eggs in small that had been freshly mowed.

"We found that if we mow small amounts of these areas in June or July, we see increases of anywhere from three to 10 times more eggs per stem on the regrowth, with fewer predators around to eat them," Haan said.

In followup experiments, scientists plan to use strategic mowing on a larger scale.

"We need to see how this approach affects other wildlife, such as pollinators and birds, in larger settings around the state," Haan said. "This could eventually lead to management recommendations to transportation departments in Michigan, and other midwestern states, as well as landowners hoping to attract more monarch butterflies to their property."

Researchers suggest anyone with milkweed in their backyard try mowing or trimming a third of the patch during mid-June. Another third can be trimmed in mid-July, allowing a third to remain full-grown.

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