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  • Writer's pictureJohn Chapin

Multiplying Monarch Populations

monarch butterfly on milkweed flowers

With the alarming decline in monarch butterfly populations in North America, many people now plant milkweed, which as even schoolchildren know, is the food plant for monarch butterfly caterpillars. There is a nationwide movement to help this iconic butterfly increase its population. There is a field near our house in rural Danville that has always had a large patch of native common milkweed. We always notice butterfly activity in this field, increasing in late summer into fall.

One year recently, we were alarmed when the owner of the field mowed everything to the ground in late July, not sparing the milkweed plants. However, within just a few weeks, the milkweed sent up new growth from the roots, seemingly filling the field even more densely. By the end of August, the field was absolutely swarming with adult monarchs feeding on the flowers as well as laying eggs on the fresh foliage of the rejuvenated plants.

monarch caterpillar eating leaf
Photo by Britannica

Many people don’t realize that the monarch caterpillars that hatch from eggs laid in late summer mature into the adult butterflies that make the long journey to Mexico for the winter. So, this last generation of butterflies is crucial to the population’s survival.

Now, research has shown that what we thought was detrimental to monarchs is actually significantly beneficial. People who plant milkweed are now encouraged to cut back a third to half of their milkweed plants by the middle of August, either halfway or completely to the ground, being careful to transfer any caterpillars or eggs they find to other plants. The new leaves from the fresh growth are very attractive to monarchs and, as a bonus, are temporarily free of predators.

Monarch populations are remarkably resilient and capable of tripling their numbers from year to year. It’s hoped that, with our help, the monarch can recover to stable population levels.

For fascinating information about monarch butterflies, check out these frequently asked questions.

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