In case you missed it, a monarch butterfly migration study published in the Proceedings of the National Academy of Sciences in June 2019 has troubling news for those who rear monarchs indoors.

Eastern monarch butterflies, famous for their autumn migration from North America to Mexico, have declined 80-90% in the last 20 years. To help the butterflies many people collect eggs and caterpillars in the wild and captive-raise them to increase their chances of survival. Unfortunately this well-meaning act can damage the insect’s ability to migrate.

Researcher Ayse Tenger-Trolander at Univ. of Chicago stumbled upon this when she purchased captive-bred butterflies for her monarch migration study. To measure their autumn migratory drive she placed them in a flight simulator and noted the dominant direction they wanted to fly. Wild migratory monarchs orient South. The captive-bred monarchs chose random directions, unlikely to migrate.

To further test the butterflies, Tenger-Trolander collected wild monarchs and raised a new generation indoors, mimicking outdoor autumn conditions. Here’s what she found.

Furthermore, rearing wild-caught monarchs in an indoor environment mimicking natural migration-inducing conditions failed to elicit southward flight orientation. In fact, merely eclosing(*) indoors after an otherwise complete lifecycle outdoors was enough to disrupt southern orientation.

Contemporary loss of migration in monarch butterflies, PNAS

Chip Taylor, Director of Monarch Watch, pointed out on NPR that some captive-bred monarchs do make it to Mexico, but added that “The real reason for raising monarch butterflies is for the enjoyment, the education. [T]he idea of individuals saving caterpillars as “monarch rescue” is misguided. “That’s simply not going to work as a way to boost the population,” says Taylor. “What we really need to do is to improve the habitat.”

We’re learning that monarch migration is complex and very fragile. It’s easy to break it in a single generation.

(photo by Kate St. John)

(*) “eclosing” means emerging from the chrysalis.

Monarch butterflies are famous for migrating long distances from North America to Mexico but they’re not the only butterfly that travels far. Red admirals migrate, too.

Red admirals (Vanessa atalanta) occur in Europe, Asia and North America. Though the European population can hibernate, red admirals on this continent migrate south to places where their favorite host plant — stinging nettle — grows throughout the winter. In eastern North American they spend the winter in south Texas.

Over the winter a new generation of red admirals matures to fly north and repopulate the continent. We usually don’t notice them but in the spring of 2012 hot weather came so fast that red admirals passed through Presque Isle State Park in a couple of days on mass migration.

On Throw Back Thursday read about the amazing number of red admirals in 2012 in this vintage blog: Mass Migration.

Why don’t we see them migrating more often? Perhaps they’re traveling high above our heads. According to Wikipedia: “During migration, the red admiral flies at high altitudes where high-speed winds carry the butterfly, requiring less energy.” Oh my!

(photo from Wikimedia Commons; click on the caption to see the original)