As a child, I was fearful of the prehistoric-looking dragonflies that swooped over my head as I floated in the swimming pool. I had been told they could sew up my lips, after all. That turned out to be a myth, thankfully. Dragonflies are harmless. So now that we've established the fiction, let's take a look at 10 cool facts about dragonflies.
1. Dragonflies are ancient insects.
Long before the dinosaurs walked the Earth, dragonflies took to the air. If we could transport ourselves back 250 million years, we would immediately recognize the familiar site of dragonflies flying in pursuit of prey. Griffenflies, the gigantic precursors of our modern dragonflies, took flight in the Carboniferous period over 300 million years ago.
2. As nymphs, dragonflies live in the water.
There's a good reason why you see dragonflies and damselflies around ponds and lakes – they're aquatic! Female dragonflies deposit their eggs on the water's surface, or in some cases, insert them into aquatic plants or mosses. Once hatched, the nymph (or naiad, in this case) spends its time hunting other aquatic invertebrates. Larger species will even eat the occasional small fish or tadpole. After molting 9-17 times, the dragonfly will finally be ready for adulthood, and the nymph will crawl out of the water to shed its final nymphal skin.
3. A dragonfly nymph breathes through its anus.
A damselfly nymph breathes with gills at the end of its abdomen. The dragonfly nymph's gills, oddly, are inside its rectum. That's right, it breathes with its butt. The dragonfly nymph will pull water into its anus, where gas exchange occurs. When the dragonfly expels the water from its rear, it propels the nymph forward, providing the added benefit of locomotion.
4. Up to 90% of young dragonfly adults get eaten.
When the nymph is finally ready for adulthood, it crawls out of the water onto a rock or plant stem and molts one last time. It takes up to an hour for the adult to expand its body. This newly emerged dragonfly, referred to as a teneral adult, is soft-bodied and pale, and highly vulnerable to predators. For the first few days, until its body hardens fully, it is a weak flier. Teneral adults are ripe for the picking, and birds and other predators consume a significant number of young dragonflies in the first few days after emergence.
5. Dragonflies have excellent vision.
Relative to other insects, dragonfly vision is extraordinarily good. The head consists almost entirely of two huge compound eyes, which gives the dragonfly nearly 360° vision. Each compound eye contains as many as 30,000 lenses, or ommatidia. A dragonfly uses about 80% of its brain to process all this visual information. They can see a wider spectrum of colors than humans. This remarkable vision helps them detect the movement of other insects and avoid collisions in flight.
6. Dragonflies are masters of flight.
Dragonflies can move each of their four wings independently. In addition to flapping each wing up and down, they can rotate their wings forward and back on an axis. This flexibility enables them to put on an aerial show like no other insect. Dragonflies can move straight up or down, fly backwards, stop and hover, and make hairpin turns, at full speed or in slow motion. A dragonfly can fly forward at a speed of 100 body lengths per second, or up to 30 miles per hour. Scientists at Harvard University used high-speed cameras to study dragonfly flight. They photographed dragonflies taking flight, catching prey, and returning to a perch, all within the a time span of just 1-1.5 seconds.
7. Male dragonflies exhibit aggression toward other males.
Competition for females is fierce, and male dragonflies will aggressively fend off other suitors. In some species, males will claim and defend a territory against intrusion from other males. Skimmers, clubtails, and petaltails scout out prime egg laying locations around the local pond. Should a competitor fly into his chosen habitat, the defending male will chase him off. Other kinds of dragonflies don't defend specific territories, but will still behave aggressively to other males that cross their flight paths or dare to approach their perches.
8. The male dragonfly has secondary sex organs.
In nearly all insects, the male sex organs are located at the tip of the abdomen. Not so in male dragonflies. His copulatory organ is on the underside of his abdomen, up around the second and third segments. His sperm, however, is stored in an opening of his ninth abdominal segment. Before mating, he has to fold his abdomen and transfer his sperm to his penis.
9. Some dragonflies migrate.
A number of dragonfly species are known to migrate, either singly or en masse. As with other organisms that migrate, dragonflies relocate to follow or find needed resources, or in response to environmental changes like cold weather. Green darners, for example, fly south each fall, moving in sizeable swarms. They migrate north again in the spring. The globe skimmer is one of several species known to develop in temporary freshwater pools. Forced to follow the rains that replenish their breeding sites, the globe skimmer set a new insect world record when a biologist documented its 11,000 mile trip between India and Africa.
10. Dragonflies are capable of thermoregulation.
Like all insects, dragonflies are technically ectotherms. But that doesn't mean they're at the mercy of Mother Nature to keep them warm or cool. Dragonflies that patrol (fly back and forth, versus those that tend to perch) will fire up their wings, using a rapid whirring movement to warm up their bodies. Perching dragonflies rely on solar energy for warmth, but position their bodies skillfully to maximize the surface area exposed to the sun's rays. Some even use their wings as reflectors, tilting them to direct the solar radiation toward their bodies. Conversely, during hot spells some dragonflies will position their bodies to minimize sun exposure, and use their wings to deflect the sun.
- Encyclopedia of Insects, 2nd Edition, edited by Vincent H. Resh and Ring T. Cardé, 2009.
- Borror and Delong's Introduction to the Study of Insects, 7th Edition, by Charles A. Triplehorn and Norman F. Johnson, 2005.
- Kaufman Field Guide to Insects of North America, by Eric R. Eaton and Kenn Kaufman, 2007.
- Dragonflies and Damselflies of the West, by Dennis Paulson, 2009.
- Dragonflies: The Flying Aces of the Insect World, by Miles O'Brien and Ann Kellan, National Science Foundation, October 3, 2011.
- Introduction to the Odonata, University of California Museum of Paleontology, accessed February 10, 2012.
- Minnesota Odanata Survey Project, accessed February 10, 2012.