As the first frost of autumn arrives, my warm weather pursuit of dragonfly watching goes dormant for the winter. I have always been fascinated by these amazingly aerobatic insects and the more I have read about them the more captivating they become. In this essay I would like to present some of what I have learned about adult dragonflies.
You may have heard stories of primeval dragonflies with wingspans of almost three feet. Those insects had a similar appearance but weren’t true dragonflies. They were actually distant relatives, the griffinflies. Those giants lived about 300 million years ago and one species has indeed been documented as having a 28-inch wingspan. That makes it close to the breadth of our pileated woodpeckers to which the Sibley field guide attributes a 29-inch wingspan. The dragonflies we see today are quite ancient however. Fossils from modern dragonfly families have been found revealing that they soared in Jurassic skies as dinosaurs prowled the earth.
Like other insects, dragonflies have three part bodies. The head is all about vision and eating. Eighty percent of a dragonfly’s brain is channeled into processing visual information. Massive wrap around compound eyes are composed of up to 30,000 simple units called ommatidia and provide almost 360 degrees of vision. Human eyes have three light sensitive proteins (opsins) that allow us to see red, green, and blue and those hues combine to create the many colors we perceive. Recent research revealed that the eyes of dragonflies have eleven to thirty-three opsins and that gives them the added ability to see into the ultraviolet spectrum. In addition, they can visualize how light is polarized and may use this ability as a navigational tool. Their visual prowess does not end there. Dragonflies also have three simple eyes between their antenna. Those seem to have to do with sensing light intensity and the horizon to help stabilize flight. Superb vision is a big part of what makes these insects superb hunters. Their mouth-parts are also well adapted to this way of life. The main prey of dragonflies is flying insects. Their scissor-like jaws immediately go to work on newly caught (and very unfortunate) prey severing the wings so it cannot escape and then ripping it apart for consumption.
The thorax is primarily the center for locomotion as it provides attachment points for the legs and wings. A dragonfly has six legs but ironically, it cannot walk. The spiny legs are instead well adapted for prey capture, grasping onto landing sites, and for males, latching onto a female during mating. The four wings that extend from the thorax are another major component to its predatory lifestyle. They operate independently from each other and allow forward, backward, straight up/down, and sideways flight and for hovering. Dragonflies are fast! Cruising speeds have been documented at 24 mph and the top speed for one species was clocked at 38 mph.
A dragonfly’s abdomen contains organs of digestion, reproduction, and surprisingly, respiration. If you find a perched dragonfly and can get close enough, watch the abdomen and note its bellows-like movement as air passes in and out through the respiratory spiracles. Males have clasping appendages at the end of the abdomen that grip the female during mating. Those appendages are species specific and are thought to form a precise fit with females of the same species to prevent the insect from mating with a female of another species. It is not unusual to find an adult female with eye damage or perforation due to injury caused as the male grasped her and fitted the appendages into place.
Dragonflies are fascinating creatures and in this essay we’ve barely scratched the surface of information known about them. Here in Island County, we have at least 18 species. I have really enjoyed submitting my sightings and photos to Odonata Central (http://www.odonatacentral.org/) to help document what species can be found here and when they are present. There are quite a number of wetlands, lakes, and ponds in our area that are reliable places to find them when the warm sunny days of spring, summer, and fall return. Some of my favorites are the Rocky Point/Joseph Whidbey State Park area, Earth Sanctuary, Deer Lagoon, and Deception Pass State Park’s Cranberry Lake. For help identifying the dragonflies you find, I recommend Dragonflies and Damselflies of Oregon by Cary Kerst and Steve Gordon and Dragonflies and Damselflies of the West by Dennis Paulson. James S. Walker (“the Dragonfly Whisperer”) is known to many who have attended Sound Waters in recent years as he has given classes there. He has recently published a new book, Common Dragonflies and Damselflies of the Pacific Coast which promises to be another great resource.
For more about how a dragonfly reacts to visual stimuli, check out this excellent video by the BBC: https://www.bing.com/videos/search?q=dragonfly+vision+video&&view=detail&mid=94E35828F8D43F0BF5B594E35828F8D43F0BF5B5&FORM=VRDGAR
Another very worthwhile video illustrates how Harvard researchers use high speed videography to learn more about dragonflies:
All photography by Mary Jo Adams