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Weather Radars Reveal an 80 Percent Chance of … Dragonflies? – 

Birds aren’t the only ones who seek warmer climates during the winter months; many species of dragonflies also migrate each year. In fact, as many as 50 of the estimated 5,200 dragonfly species in the world migrate, following topographical features such as rivers and coastlines. Experts know little about dragonfly migration, but they are beginning to monitor patterns, noting that cold fronts usually trigger the migration process.

Each spring and fall, large dragonflies called green darners fly across North America. A green darner can travel as far as 900 miles on its two-inch wings, fluttering from Canada to the Gulf of Mexico. They are some of the most abundant dragonflies on the continent — but few people notice this mass migration.

Green Darner Dragonfly-Anax junius

Unlike monarch butterflies and songbirds, whose long-distance migrations draw crowds, green darners are inconspicuous travelers. These dragonflies rarely migrate in huge swarms. Radiant up close — emerald green at the thorax, splashes of blue on the abdomen — a three-inch-long dragonfly becomes a speck at a hundred yards. Even dragonfly experts have had little luck observing this cross-continental journey.

Citizen Science data has allowed scientists to figure out what types of natural cues, like temperature, give the dragonfly larvae the signal to emerge and migrate. Between February and March, the first generation of dragonflies emerges from ponds and lakes in the southern United States, Mexico and the Caribbean. Then those resilient first-gen bugs travel hundreds of miles north as, making it to New England or the upper Midwest by May. When they get there, they’ll lay their eggs and die.

green darner dragonfly migration map

The lives of the next generation are just as incredible. While some of those second generation insects will hang out and overwinter in ponds and lakes in the north during their nymph stage, many will reach maturity and head south between July and October.

When those insects reach the south, they deposit another batch of eggs, which mature into a third generation that will live a non-migratory life over the winter on the coast, producing the eggs of the dragonflies that will migrate northward again in the spring.

Doug Kahn, a meteorologist at the National Weather Service in Cleveland, saw several bluish masses shifting and swelling over Ohio. The undulating blobs on the radar were not storm clouds or a weather system, but a swarm of dragonflies.

“There are millions of them,” he said. “That is why you can see so many of them on the radar.”

Swarms of dragonflies captured on radar by the National Weather Service in Cleveland.CreditCreditNOAA

Radars like the ones used by the Weather Service are often used to track the seasonal movements of bees, birds, flies and other airborne creatures. Migration is common in insects and birds, according to Sara Kross, director of the master’s program in ecology, evolution and conservation biology at Columbia University.

“There are species that will migrate and those that will move due to the weather patterns,” Dr. Kross said.

“We now can predict when we will see waves of birds all through radar and knowledge,” she continued. “Right now, because of radar, we can see it happening in real time.”

It is the same science used to detect precipitation. “Insects are usually kind of longer” than a raindrop or a snowflake, Mr. Kahn explained. That results in a higher ratio of length to the height.

“If we see a thunderstorm, the radar sends up a beam and it hits clouds in the sky and it returns that imaging to us,” Mr. Kahn said. The only difference with insects is that the radar bounces off the millions of tiny bodies in the swarm.

It appears none of the swarm occurrences are rare.

“Picking up on the sheer scale of migration is something you can deduce from data,” Dr. Kross said. “But having radar really shows the intricacies of those movements.”

Nature walks are wonderful. But you don’t have to travel to special location to enjoy Mother Nature. There is so much to see in your own neighborhood or even in your own back or front yard. Get a guide-book of the wildlife in your area and learn the calls of birds and frogs and toads. So many times I hear a bird that lets me know what I am looking for in the trees.

Have a wonderful week from Michelle!

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