Insects and other arthropods like spiders and centipedes seem so a part of our gardens, that often, unless they are nibbling our chard or otherwise causing a nuisance, we don’t even notice them. In the cool of autumn arthropods become conspicuously absent as they die or retreat into dormancy. This may be a positive development for some; but for others, pine for the pitter patter of little feet.
For the amateur entomologist, fall is one of the best times of the year to get a closer look at members of the order Odonata: dragonflies and damselflies. In summer, these large, swift insects are almost impossible to miss as they maneuver deftly on the wing. For those of you who have collected insects to identify and otherwise inspect them, you know how difficult dragonflies are to net. Their large compound eyes are composed of between 10 and 30 thousand lenses–no wonder darners are darned hard to catch. Late in the season when the adults are weak and disoriented, we have the advantage. When collecting, inspect these winged wonders immediately and note or photograph eye and body colors. As the life drains out of them, a damsel in distress loses its vibrant, identifying hues.
Most dragonflies live 6 to 10 weeks and have a single generation of offspring a year—with eggs or juveniles over-wintering in water. Thus dragonflies and damselflies are naturally found near lakes and streams. All arthropods breathe via gills, trachea or spiracles—not with lungs. The young Odonata nymphs, as the waterborne juveniles are called, breathe underwater by gills in their rectum. And amusingly enough, move through the water by forcing water from their anus. Jet propulsion, if you will. See: studying insects can help you with a lull in cocktail party conversation or inspiration for the word game Balderdash.
The largest dragonfly known from fossils lived 250 million years ago and had a wingspan of more than 2 feet. Of the 435 known species of Odonata in North America today, body length ranges from a more comforting 1 to 5 inches. The two suborders that make up Odonata are the dragonflies (Anisoptera) and damselflies (Zygoptera) which are easy to tell apart with the naked eye. Dragonflies have hind wings that are wider than their front wings, especially where they meet the body. Their eyes are closer together than the damselflies, whose more distant eye separation resembles as a dumbbell.
When Odonata perch on rocks or plants, they do so to adjust their body temperature; angling themselves according to sun and breeze. When at rest, dragonflies stand out from damselflies by spreading their wings out flat, while damselflies hold their wings together above and in line with their abdomen. Damselflies’ front and back wings are of similar size and shape, but narrower where they connect to the body at the thorax.
Since juvenile and adult Odonata feed on insects, they are considered beneficial to humans and are harmless to us in that they neither bite, nor sting. And anyone who has ever been mesmerized by the winged antics of dragonflies will attest: their graceful beauty invites a closer look.
© Colleen Miko, 2010.