For years, lovers of the orange and black monarch butterflies that make Michigan home in the spring and summer have planted milkweed to help the declining species along. In an odd quirk, milkweed is the only plant monarch caterpillars eat, and the plant's broad leaves are sought out by the butterfly for egg-laying.

New research out of Michigan State University, however, says monarch-lovers should consider chopping down at least some of their milkweed plants later in the summer.

"From a monarch's perspective, they need milkweed, but not all milkweed stems are equal," said Nate Haan, a postdoctoral research associate in MSU's Department of Entomology.

"When they are flying around looking for the best places to lay their eggs, they are seeking out younger, more tender stems that haven't flowered yet. As summer progresses, those stems get more and more hardened."

Haan's research, published in the peer-reviewed, scientific Journal of Biological Conservation, shows that mowing a third of milkweed patches in June and July, respectively, resulted in more monarch butterfly eggs laid on the regenerating milkweed than on the remaining, undisturbed third of milkweed plants.

"Milkweed is really robust," he said. "If you chop some down in the middle of summer, in a couple of weeks it will send up new shoots."

It's a phenomenon that has been observed for generations, Haan said — "even some observations going back to the 1800s that after hay fields got harvested, the fields got mowed, and the milkweeds that came back up had a lot of monarch eggs on them."

But no one had ever tested the anecdotes in an empirical study before, he said.

The mowing has an added benefit, Haan said.

"Monarch eggs and caterpillars get eaten by predators such as ants and spiders," he said. "We wondered if the disturbance of the milkweeds would also knock back predator populations, providing a window in time where predators are less abundant and the eggs and caterpillars are better allowed to thrive. We found that was the case, too. It takes a few weeks for the predator populations to build back up" after a milkweed mowing.

This process happened naturally for most of the 20th Century, as milkweeds typically grew in agricultural fields and were taken down during mechanical harvesting, Haan said. But changes in the types of herbicides farms use have all but wiped out milkweeds in the fields, he said.

The monarch butterfly is unusual. It's the only known butterfly to make a two-way migration to a warmer, Southern winter home, as migratory birds do. Butterfly generations typically live about two to six weeks, with Michigan seeing about two or three generations of monarchs beginning in May and lasting through the summer. But the last generation, around September, survives longer, making the long journey to an area of Mexico where millions of monarchs overwinter.

When spring comes, so does the northward trek, with several generations of monarch butterflies living, breeding and dying, as they make their way back to their summer habitat throughout the northern U.S. and southern Canada.

The population in recent years has suffered a disturbing decline, with only 1.7 acres of their Mexican winter grounds covered in the winter of 2013-14. Weather, pesticides and habitat destruction are suspected factors. The last few years, however, monarchs have made a comeback, with this winter in Mexico the best in at least a decade — almost 15 acres of monarchs.

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Brenda Dziedzic of Westland, a conservation specialist for the nonprofit Monarch Watch in Michigan and author of the book, "Learn About Butterflies in the Garden," said she is not surprised by the findings of Haan's research.

"It absolutely makes sense," she said.

"Monarchs, if you have a (younger) plant, the butterfly will lay its eggs on that because it's more tender. Only if there's nothing else around will they lay their eggs on the larger, tougher leaves."

MSU researcher's tips for helping monarch butterflies thrive in Michigan:

Plant milkweed, which is vanishing in its typical, natural habitats. "The more milkweed we plant, the better," said Nate Haan, postdoctoral research associate in Michigan State University's Department of Entomology. Seeds for milkweed plants native to Michigan can be purchased online or at some local greenhouses.

Don't misuse his research. Haan doesn't want people taking a lawnmower to the entirety of their milkweed stands this summer. Instead, use a weed whip to take down about one-third of an area's milkweed plants around mid-June; then do the same to a different third of the plants in mid-July. "What I guess will happen, on that new growth, is you'll see a lot more eggs and caterpillars," he said.

Contact Keith Matheny: 313-222-5021 or kmatheny@freepress.com. Follow on Twitter @keithmatheny.