Migratory journey of the dragonfly is completed by three generations

Researchers have analyzed and described the full life cycle of a dragonfly for the very first time. The paper details the migration patterns of the common green darner, which is a large, abundant dragonfly found across North America.

The research team found that it takes the green darner three generations to complete its annual cycle. One generation migrates north in spring, the second generation migrates south in fall, and the third generation remains in the southern part of the species’ range over winter.

With a wingspan of just three inches, the insects manage to migrate an average of 373 miles, with some individuals covering more than 1,553 miles.

Study senior author Colin Studds is an assistant professor of Geography and Environmental Systems at the University of Maryland, Baltimore County (UMBC).

“We know that a lot of insects migrate, but we have full life history and full migration data for only a couple,” said Professor Studds. “This is the first dragonfly in the Western Hemisphere for which we know this. We’ve solved the first piece of a big mystery.”

Even though the common green darner is abundant and is not a threatened species, understanding their life cycle is important in a global context.

“There are massive insect declines going on around the world, so understanding these complex biological patterns is essential to determine why different populations might be declining,” explained study co-author Peter Marra.

The investigation was focused on 21 years of citizen science data, over 800 dragonfly wing specimens from museums, and specimens caught in the wild.

The team took a creative approach to their analysis by looking at the prevalence of different forms of hydrogen in the dragonflies. In the atmosphere, the concentration of three forms of hydrogen shifts with latitude. The hydrogen ratio in a tiny portion of the dragonfly’s wing reveals where it was born, and this information enabled the researchers to identify the three-generation migration system.

The team also discovered specific cues that determine whether dragonflies choose to migrate or to emerge as flying adults after their aquatic juvenile stage. Temperature was found to be the biggest cue, and the experts noted that dragonflies both emerged and initiated migration at around 48 degrees Fahrenheit.

Professor Studds explained that the research is the beginning of a long path toward better understanding insect migrations. The discovery of the three-generation process, with two migratory generations and one resident was “remarkable” in itself, he said. “How it actually happens is a tremendous new mystery that brings together ecology and evolution, and there’s a lot more to understand.”

The study is published in the journal Biology Letters.

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By Chrissy Sexton, Earth.com Staff Writer