Sunday, September 26, 2010

Dragonfly invasion

Common Green Darners, Anax junius. Male (right) holding female as she oviposits eggs into a cattail leaf.

This has been an absolute invasion year for dragonflies in Ohio, and elsewhere in the Midwest. Swarms big and small have been widely reported, some numbering into the thousands of individuals. I had the good fortune of seeing one of these green darner feeding frenzies a few weeks back, in Ross County. Several thousand dragonflies were darting to and fro over meadows along a floodplain, creating a surreal scene.

Stimulated by word of numerous other sightings of migrant darner swarms, I wrote an article that was published in a number of newspapers throughout the state, and that led to even more reports. One of the more interesting came from Kim McCoy, of Fayette County, who witnessed a massive feeding swarm on her property on September 15. Not only that, but she made a video that captures the scene. View the vid RIGHT HERE.

My column, with more info about migrant dragonflies, is below:

Invasion of the Dragonflies

A fantastic insect invasion has been occurring recently. No worries – a plague of locusts hasn’t descended, nor are killer bees overrunning Ohio.

Our visitors are dragonflies: common green darners, Anax junius. Large swarms of these jumbo fliers have been reported from numerous Ohio locales and elsewhere in the Midwest in the past week or so.

Common green darners are easily recognized. They are one of the largest of the 160+ dragonfly species that have been found in Ohio. From stem to stern, a good-sized darner can measure 3 ½ inches, with a wing span of four inches. The thorax (main body) is a distinctive pea green. Males have a turquoise-blue abdomen (tail); in females the abdomen is rusty-brown.

This species is a common inhabitant of Ohio’s ponds and wetlands, and is found in all 88 counties. Like other dragonflies, their larvae – nymphs – are strictly aquatic. The bizarre, alien-looking nymphs remain under water for a year, hunting small animal life. When tripped by some internal alarm clock, the nymph emerges from the water shortly after dusk, climbs a plant, and begins an amazing transformation. The nymph’s husk is slowly split open by the young adult – termed a teneral – as it pushes its way out. Once it has broken free of its larval shell, the teneral darner quickly hardens and expands. By daybreak, the transformation into an adult dragonfly is complete and the green darner is ready to take flight.

And take flight they do. Incredibly powerful flyers, green darners spend much of the daylight hours on the wing, jagging about at impossible speeds as they snatch small flying insects from the air. While gnat-sized bugs form the bulk of their diet, the burly dragons can take down much larger fare. When opportunity allows, they’ll grab large horseflies, bees, and lesser dragonflies. They have even been reported to take hummingbirds!

A big mystery shrouds the common green darner. This is one of our highly migratory insects, as is the monarch butterfly. However, the movements of green darners are not nearly as well understood as those of the monarch, and scientists are still unraveling the secrets of darner migration. In late summer, massive “flocks,” perhaps better called swarms, are sometimes seen. This year, darner swarms have seemingly been more numerous than usual, with many scattered reports.

It is a striking sight to witness hundreds or even thousands of these large dragonflies swirling about. Sometimes they are seen high aloft, moving together on a steady southward trajectory. On other occasions, swarms descend to low levels and actively feed over meadows and other open areas.

Where are they going? No one is sure, but it’s possible that the darners are moving to warmer climes of the southernmost U.S and Mexico. Green darners also appear to migrate back north in the spring, much as birds do.

A lot remains to be learned of dragonfly migration, and observations of large swarms are helpful to researchers. If you have witnessed a dragonfly swarm, please report it to Jim McCormac at the Ohio Division of Wildlife: or 614-265-6440. Please note the date, time, location, and ideally an estimate of the number of dragonflies.

Green Darner, female


Doug Taron said...

We had a similar huge swarm on September 12 at the Chicago lakefront. I remember the date, because it coincided with the Peggy Notebaert Nature Museum's annual bug fest, and there were thousands of them swarming right outside of the museum's front door. Good timing! The nesxt day they were gone.

Jim McCormac said...

Thanks for the report, Doug. I had heard about some of those incredible swarms along Lake Michigan, must have been an amazing spectacle.


Trendle Ellwood said...

Yes! Dragonflies Yes! It is Dragonfly Year! I so enjoyed reading your comments on this. Thank You Jim! I wrote about my August dragonfly experiences on my blog, I would love to share.

Anonymous said...

In Pass Christian, Mississippi, Oct 13 at sunset my husband and I witnessed a dragonfly swarm that last for at least two hours where easily hundreds of dragonflies flew over our heads towards the sunset and the Bay of St. Louis. As darkness approached they continued to fly overhead, but we finally walked away so not sure how long they continued to fly. It was amazing.

Anonymous said...

September 2, 2011 We have a big swarm in our backyard right now. They are flying high up and down by the ground. Ashley, Ohio They are all over and it is so neat to see. My sister over in Radnor, Ohio saw a big swarm on her walk yesterday too! At least 100 of them.

Anonymous said...

We had a large swarm on September 12, 2013 in North Newark, Ohio. Probably hundreds of them flying North to South.