In mid-August a few years ago, I was trying to find out where the purple martins were feeding before they assembled to stage in great numbers at dusk among the common reeds on the Maurice. That year they were roosting south of the Mauricetown Causeway Bridge. When I got to Noble Street just west of the Mauricetown Fire Hall, between U.S. Silica’s mining ponds, I was met with a staggering number of darners (one of a number of large dragonflies). They were making passes over the road in the thousands.
They would pass perpendicularly rather low to the road and then rise above the trees. This created a rollercoaster-type effect. It was truly a feeding frenzy. The mixed flock included various-sized dragonflies but the large darners really stole the show. It was mesmerizing.
I thought I would find the martins around such a large congregation of dragonflies since they are one of their favorite prey species. But alas, I did not. The two species do have one commonality: Both martins and dragonflies will catch and eat their food only in flight.
I remembered once reading that biomechanics studied dragonflies to experiment with aircraft, hoping to make something as maneuverable and efficient as the dragonfly. It can fly straight up and down, hover, and even mate on the wing. Its ability is unsurpassed when it comes to moving through the air.
On display at the CIA Museum in Washington, DC is an early spy device that was made during the Cold War, circa 1970—a robotic dragonfly darner. This was the first of many insect robotic spy devices. Popular Mechanics (Feb. 18, 2020) covered the release of mechanical drawings by the CIA, for the first time in 50 years, showing the details of the “Insectohopter.” Retroreflectors, or tiny beads, mirror laser light, causing vibrations that can be analyzed to extract sound from that light—a microphone. This is how the CIA eavesdropped.
Back to the swarm. Christine Goforth at the North Carolina Museum of Natural Sciences has been studying swarm behavior, when hordes of dragonflies congregate, feeding on small prey insects. She heads a citizen science activity called “The Dragonfly Swarm Project.” They have found dozens, millions, even billions flying in a group, especially during migration. Individuals clock in at 30 mph! Migrating groups can fly in flights 50 to 100 feet above the ground and in such numbers as to be picked up by radar.
Migration normally occurs in August and September. Two groups of dragonflies are migrators in North America—the darners and the skimmers—and 16 species comprise these groups. In the adult form most dragonflies live for only two to four weeks, while migrating species may live for a few months. Their larval stage—or nymph or naiad—is the longest part of their lifecycle, lasting a month to five years, depending on the species and habitat conditions.
The larvae climb out of the water on emergent vegetation (partly aquatic submerged plants) to molt or metamorphose into the flying adult. The shed exoskeleton, or exuviae, often stays on the vegetation as an empty cast. This shedding process takes place eight to 17 times before the full metamorphosis, and it requires a few days to a few weeks for the body to become firm and develop its true colors once more. Adults then lay their eggs on the water and the lifecycle begins again (Stokes).
Scientists have attached miniature transmitters to darners, and discovered that green darners from New Jersey traveled every third day, averaging 7.5 miles. One individual logged 100 miles in one day! A species called globe skimmer has the longest flight of any insect in migration—11,000 miles across the Indian Ocean and back (Smithsonian magazine).
Dragonflies and damselflies are of the order Odonata. Neither is a fly; they also have six legs and three body parts—head, thorax, and abdomen; while flies have two wings, dragonflies have two sets of two. The word dragon is used to describe them because of their toothed jaws. Odonata derives from the Greek word odon; essentially tooth.
Damselflies rest with their wings primarily together, but dragonflies perch with wings open and spread horizontally. Damselflies will eat prey on surfaces of vegetation. Most dragonflies’ eyes touch but damselflies’ eyes are clearly separated. Their lifecycles are very similar.
Dragonflies’ eyes take up nearly all of the head; their heads can be moved 180 degrees side to side, and 40 degrees up and down. Their compound eyes are six-sided units, and there is an additional three smaller simple eyes called ocelli, used to detect subtler motion. They are deadly hunters eating greenheads, strawberry flies, gnats, midges, and mosquitos; one species is even known to eat hummingbirds. Consuming these insects makes them of great value to people. In their larval stages they eat mosquitos, tadpoles, fish, other larvae, and other dragonflies. They do not attack people, but if held they can bite.
There are about 5,000 species of dragonflies, with 435 species found in North America. From fossil records we know they have existed for around 300 million years, predating dinosaurs. Some fossils reveal it to be the largest insect ever to exist.
Called Meganeuropsis, it was discovered in France in 1880 in the form of various specimens measuring five to 24 inches. Some scientists believe they achieved these sizes during the Paleozoic era because of higher oxygen levels.
Of New Jersey’s 180 species of dragonflies and damselflies, 30 are at risk of extirpation. Development pressures, habitat, and water quality affect their reproductive success and impact species less tolerant of degradation.
The months or years that they spend as larvae in the water allow them to bioaccumulate toxins. Later this month CU volunteers will collect nymphs for mercury analysis as part of a national water and habitat quality study at the University of Maine, in partnership with the U.S. Geological Service, the Schoodic Institute, and the National Park Service.
Backyard ponds help dragonfly populations and they are valued predators of pest species; sometimes they are referred to as “mosquito hawks.”
My experience on Noble Street was not unique. I have seen large assemblages of dragonflies hunting for food. But the way they almost seemed to roll over the trees and road is forever etched in my mind.
Field Guide to Dragonflies and Damselflies of NJ, A. Barlow, D. Golden, and Jim Bagma
Beginner’s Guide to Dragonflies, Stokes
Popular Mechanics, February 2020