Science, Tech & Environment

After years on the brink, it might be comeback time for monarch butterflies


A mature monarch on a milkweed flower.


Ellen Woods

This past winter, the future of the monarch butterfly looked grim. But now, a comeback might be brewing.

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For three years in a row, scientists saw record low numbers of hibernating monarchs in Mexico, the site of their southern migration. This winter’s numbers were the lowest on record. That had researchers worrying that monarchs were on the path to extinction.

But now, initial summer breeding numbers are providing good news. Anurag Agrawal, Professor of Ecology and Evolutionary Biology at Cornell University, has been tracking the Monarchs and says recent signs are encouraging.

“Our first numbers for how the monarchs are doing this year comes from Texas,” he explains. “The tens of millions of monarchs that were overwintering in Mexico, in the mountains of Michoacan, fly to Texas and lay eggs there ... Caterpillars develop on the Texas milkweeds, and those adults then pass away. That first generation in Texas did well, and they've moved north.”

Monarchs typically breed three to four generations each year, and summertime is their opportunity to rebuild the population. They’re pretty good at it if given the chance.

“There's tremendous reproductive potential in the monarch butterfly,” Agrawal says. “A female has about a thousand eggs in it, so in the field she might deposit four to five hundred of those. Quite remarkably, if all five hundred were to survive, one female and one male could repopulate the tens of millions of butterflies we expect to see each year.”

Agrawal says researchers hope to see the monarch population continue to build over the summer. But they won’t know the real state of the population until the time of the southern migration.

Monarchs have even gotten some unexpected government attention. In recent year, the agrictural and economic effects of "colony collapse" among honey bees have led government officials to take notice of the problem.

President Barack Obama recently issued a formal presidential memorandum requiring 14 federal agencies, including the Environmental Protection Agency and the Departments of Agriculture, Transportation, Defense, Education and Energy, to work together to create a strategy for maintaining bee and pollinator health. The memorandum specifically mentions the monarch butterfly.

Agrawal says the monarch’s inclusion is important, but also kind of funny.

“The amusing part,” Agrawal says, “is that we know from the biology of milkweeds, which are the host plant of the monarch butterfly, and from [the Monarch’s] general biology, that they are not particularly good pollinators. They're doing very little of the pollination of milkweed or other plants.”

If they’re not important pollinators, then why did President Obama include them in his memorandum?

“In my view, the attention to the monarch comes from two sources,” Agrawal says. “One: millions of people all over the continent are appreciating their natural beauty. [Two], because it travels across three nations — from Canada through the US to Mexico — the environmental health of our continent is, in a way, reflected in the annual cycle of the Monarch.”

“If this butterfly can't complete its lifecycle, then we're doing something wrong as a continent,” Agrawal concludes, “because we aren’t providing a sustainable habitat where the butterfly can do its annual migration.”