During the Permian geologic period, 300-250 million years ago, all of the Earth’s land was a single supercontinent known as Pangaea. In the drier climate, ferns gave way to the first modern trees – conifers, ginkos and cycads. It was the time before dinosaurs, when amphibians still ruled the land and giant cockroach-like insects scurried underfoot. It was also the time that odonata first appeared on the Earth.
Millions of years later, after two major global extinctions, odonata still live on. They are the damselflies, with slender bodies shimmering iridescent and wings folded politely overhead, as well as the dragonflies, whose bodies seem almost too large for their gossamer wings to carry. Today, there are 5,500 to 6,500 dragonfly and damselfly species in the world, including 140 that live in Minnesota.
Most people consider dragonflies and damselflies to be terrestrial flying insects, but in fact, they spend more than half of their lives in the water. During the summer and early fall, adult odonatans lay eggs in wetlands, lakes and streams. Once they hatch, the larva, called nymphs, continue to live in the water for anywhere from two months to five years. During this time, they are virtually unrecognizable to all but the most astute citizen scientist. Their bodies, drab, brown and wingless, blend in with the underwater mud and muck, and they usually stick to places where reeds and other aquatic plants provide cover.
Though beautiful, both dragonflies and damselflies are fearsome predators. They dine on mosquitoes, midges, butterflies and moths. Their larva, no less deadly, eat other aquatic insects and sometimes even tadpoles and small fish.
Unlike butterflies, dragonflies undergo a process known as incomplete metamorphosis. While living in the water as nymphs, they will molt as many as 12 times as they grow. Dragonfly “instars” look the same as one another – six legs and three body parts that blend together like one fattish body – but grow progressively larger like nesting dolls. Damselfly larva are longer and thinner and have gills at the tip of their abdomen that look like three-pronged tails. If you look carefully along the edges of lakes and ponds at this time of year, you’re sure to find some of the exoskeletons left behind by dragonflies that have completed their transformations to become flying insects.
Odonata are not the only insects to begin their lives in the water. Mayflies, stoneflies, and caddisflies are a favorite food for trout and also considered to be bioindicators for healthy rivers and streams. Up north, the mayfly hatch is in full force right now.
Pest insects including mosquitoes, biting gnats, and biting black flies also lay their eggs in the water, which has led many people to worry that mosquito control might harm dragonflies and beneficial insects. Happily, research has shown that Bti and Methoprene (two kinds of bacteria found in soil that are used by Metropolitan Mosquito Control and in “mosquito dunks”) keep mosquito and biting gnat larva from growing, without impacting other insect species.
After completing metamorphosis, damselflies and dragonflies leave behind an empty exoskeleton.
Dragonflies and damselflies are emerging by the thousands this month, like a fleet of tiny dragons from a land before modern time – green darner, ebony jewelwing, orange meadowhawk and more. They’ll grace us with their beauty for a few months longer before laying eggs at the water’s edge and beginning the cycle anew.
Tread carefully if you find an ugly bug in the water this summer – it could be a baby dragonfly that’s just waiting for its time to shine.