Why were there so many dragonflies along the Chicago lakefront this weekend?
CHICAGO — “It’s like an invasion!” a woman giggled as she lowered her head and launched her bike through a swarm of dragonflies on the lakefront trail.
These large-eyed insects with nearly 4-inch wingspans flew among the crowds gathered along North Avenue Beach and Belmont Harbor to watch the annual Air and Water Show.
“They’re putting on their own air show,” an onlooker said.
While it certainly looked that way as the iridescent green, blue and red dragonflies darted through the air a couple of hundred feet below the Blue Angels, they were more likely migrating, eating and mating.
The lakefront welcomed a swarm of green darners making their biannual migration to warmer climates last weekend, said Allen Lawrance, curator of entomology at Chicago’s Peggy Notebaert Nature Museum. The shoreline provides a natural path for them to follow on their journey from Canada to the Gulf of Mexico.
That they’re taking a rest in Chicago is also a telling sign that the lakefront is healthy, said Jessica Ware, associate curator of invertebrate zoology at the American Museum of Natural History in New York.
Dragonflies are the top predators in the insect food chain so, if they loiter anywhere, it’s because that ecosystem is biodiverse. For dragonflies, that translates to lots of good menu options. Their favorite snacks are mosquitoes and various flies.
“Seeing large swarms is terrific,” Ware said.
Green darners also mate during the pitstop, leaving behind eggs that will hatch and grow in nearby ponds and wetlands, such as Lincoln Park’s North Pond and Alfred Caldwell Lily Pool. This new generation will emerge alongside dozens of other Chicago-native dragonfly species in the spring, Lawrance said.
Where exactly the current influx of migratory dragonflies came from and are going, however, is a bit of a mystery. Researchers think the green darners fly diagonally across North America, from Canada to the Gulf states. But, they’re using recent advances in insect genetics to better piece together dragonflies’ migratory journeys. Since dragonflies lay eggs as they migrate, they leave a trail of DNA that scientists can analyze.
“We’re going to be able to solve this mystery a lot faster now,” Ware said. “When we look at the DNA of these species, we can see that green darners across the United States share a lot of genetic information, east to west, north to south.”
Previously, scientists would write numbers on dragonflies’ wings and hope another scientist would find them later along their route.
However, climate change will likely make the migratory patterns scientists uncover today different from what they would have found decades ago. Many dragonflies are believed to migrate according to wind patterns. So, as climate change shifts weather patterns, migratory patterns will likely shift too.
Dragonflies are already responding very quickly to climate change, according to Ware. The geographic range of the average dragonfly species is expanding quickly. Many species are moving farther north in response to rising temperatures. Droughts and unpredictable rainfall will also affect the pond and wetland ecosystems where dragonflies spend their infancy and lay their eggs, Lawrence said.
Ware said it’s serendipitous that the green darner swarm happened to pass through Chicago during the Air and Water Show and hopes it brings more attention to them. While they travel across the continent twice a year, they often stop in Chicago on the weekdays when everyone is cooped up in their offices. One of the last times green darners sparked such curiosity and excitement was when they passed through during Lollapalooza in 2015.
Chicagoans can help researchers track dragonflies’ migratory patterns and population levels by sharing their observations on Odonata Central or joining the Illinois Odonate Survey. Similar citizen-science programs significantly contributed to our current understanding of monarch butterflies’ migration patterns.
Chicago Tribune’s Adriana Pérez contributed.
____
