A team led by Ecologist Michael Hallworth from the Smithsonian Migratory Bird Center has uncovered new information about the dragonfly's migration patterns, published in Biology Letters.
It had previously been difficult to study the migration patterns of the brilliantly coloured dragonflies as tracking devices weren’t small enough to attach. Even the most miniature tracking device weighs some 0.3 grams, twice the weight of a green darner.
Instead, Hallworth and his team instead studied hydrogen patterns on the dragonflies, including more than 800 live insects and historic specimens from natural history museums which dated back 140 years. The scientists also drew on reports on the first arrivals of the dragonflies by teams of citizen scientists.
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Migration for green darner dragonflies spans generations
They found that the first generation of the insects are born in the Caribbean, Mexico or the southern states of the United States. They emerge between February and May and begin flying north.
Some of the insects make it to New England in the north of the United States by March. When they reach this region, the darners find bodies of water to lay eggs in before they die. Some of the second generation insects spend the winter in the region before migrating, while others leave the same year. When they take flight, the second generation insects migrate south between July and October.
Late in the year, a third generation emerges in the south and spends the winter there. Finally, they give birth to another generation that restarts the process by travelling hundreds of kilometres north during the warmer spring months.
Above: Green darner dragonflies in a pond. Photo credit: US Fish and Wildlife Service Headquarters
Researchers say the study has helped unravel a “mystery” of the insect world
The multi-generational migration patterns are somewhat similar to the famously painstaking movement of the monarch butterfly though there are some subsections of the dragonfly population that make the entire migratory loop in a single generation.
Peter Marra of the Smithsonian Migratory Bird Center, the second author on the article, said there was value in studying the life cycle of insects before they disappear. “There are massive insect declines going on around the world,” he said. “Understanding these complex biological patterns is essential to determine why different populations might be declining.”
Another author, Colin Studds of the University of Maryland Baltimore Country, said that “climate change is a threat to all kinds of migration systems, and this could be one of them.” He said the study had helped add to our understanding of insect migration. “How it actually happens is a tremendous new mystery that brings together ecology and evolution,” he said.
Header image credit: Kenneth Cole Schneider