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Hand-Reared Monarch Butterflies Are Weaker Than Their Wild Cousins


Every fall, America’s eastern monarch butterflies migrate up to 3,000 miles from their northeastern homes to the mountains of Mexico for winter. To make their epic migration, the iconic orange insects run—or, rather, fly—a gauntlet. Only the toughest bugs arrive at the overwintering sites, and this year saw a 53 percent drop in butterflies that made it all the way.

Andy Davis, an ecologist at the University of Georgia, estimates that people release between 200,000 and 500,000 hand-reared monarch butterflies into the wild each year, he tells Discover magazine’s Leslie Nemo. But new research by Davis and others, published on Wednesday in the journal Biology Letters, suggests that butterflies raised indoors might not make it very far.

“Only the strongest, fittest individuals ever make it to Mexico,” Davis tells Elizabeth Preston at the New York Times. Butterflies raised in captivity, on average, have paler, shorter wings and weaker grip strength than their wild counterparts, the research found. As Davis puts it, “You’re basically bypassing natural selection.”

The new evidence builds on research published last year that found that butterflies raised indoors struggle to migrate normally, though captive butterflies raised outdoors could find their way. Per Discover, that difference inspired Davis to quantify other ways that the indoor environment affects monarch butterflies.

The research team raised just over 80 monarch butterflies indoors, and captured 41 wild monarchs to compare. While the wild butterflies had elongated wings, which are good for migration, the hand-reared cohort’s wings were more rounded. The two groups were also different colors, with the wild wings tending toward the darker, brick red and orange associated with strong migrators, while the other group had paler, yellow wings.

Lastly, the researchers measured the butterflies’ strength. It’s a delicate procedure—the researchers wrapped a short wooden rod with plastic mesh, so the butterflies could hold on to it. The rod was affixed to an electric force gauge, so that if you pulled up on the mesh, the gauge would measure the strength of the tug. Then, they brought in the butterflies.

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