The Biology of Dragonflies and Damselflies

Terminology: In some uses, the term "dragonflies" includes "damselflies" too.

Checklist of California Odonata


Dragonflies, robust insects ranging in body length from 1 to 4 inches are excellent flyers often executing rather intricate aerial maneuvers in the search for food and mates. In general they eat flies, mosquitoes, gnats and other flying insects. They do not bite. They do not attack people although it may seem that way if one decides to snatch an insect off your person. At rest the wings generally lie flat, at right angles to the body. Some species often rotate and extend their wings forward to help regulate their body temperature. In rare circumstances, young dragonflies may fold their wings over their backs. The insect you see flashing along the water's edge spent the early part of its life as a much different sort of creature in fresh water.

Damselflies, related to dragonflies, are generally smaller and much less robust. They are weaker flyers, many preferring to move from plant to plant searching for food. They eat smaller prey some of which may be gleaned from the vegetation. At rest the wings do not lie flat but are folded up over their backs sometimes in a V shape.

Life Cycle

The eggs are laid in or near water, often attached to vegetation. In some cases, the eggs are just tossed into the water. The female may become totally or partially submerged during the egg-laying process. Temporary and permanent sources of water are used.

After the eggs hatch the dragonfly nymph competes with other aquatic insects for food and the other necessities of life. Most dragonflies spend more time as nymphs than they do as the flying insects we see. The amount of time spent in the water ranges from months to years depending on the species and the conditions (5 years is the maximum I know of).

When the time is right, the aquatic nymph emerges from the water (depending on the species trees, rocks, mud, any sort of vegetation, etc. might be used). Under certain conditions, mass emergences may occur. The outer skin of the nymph splits along the back of the thorax and the young dragonfly emerges. Over the next few hours, various changes, such as wing spreading, take place during which the insect is very vulnerable to predation or disturbance. If all goes well, the insect will undergo its maiden flight, often a short relatively floppy flight away from the water, when both the wings and body have sufficiently hardened. The insects leave the water for a period up to a couple of weeks while they become sexually mature. During this maturation, the males of some species undergo dramatic changes in coloration.

Now sexually mature, the insect returns to the water to find a mate. The casual observer will tend to see males since females are less active, have more cryptic coloration and remain at or near the water for much shorter periods of time. Mating can take place in the air and be very short lived. During this process the insects are linked in a "wheel". Following the reproductive phase, there may be a period of wandering. In general, the flying insects we see live from two weeks to 3 or 4 months. Species in favorable climates and those that migrate tend to have longer lifespans.

References:
- Corbet, The Biology of Dragonflies
- Needham & Westfall, The Dragonflies of North America
- Walker, The Odonata of Canada and Alaska (3 volumes)
- any general insect book usually has some information on dragonflies


Ron Lyons (volunteer 1990-1999)
Chula Vista Nature Center, 1000 Gunpowder Point Drive, Chula Vista, CA 91910-1201