Dragonflies of the
Athabasca River Basin
Dragonflies and damselflies (Order Odonata) are strong, brightly coloured fliers with voracious appetites for several other insects such as mosquitoes, midges and even other odonates. So far 72 species have been found in Alberta (23 damselflies and 49 dragonflies). At least 16-40 species live in the Athabasca River Basin. The following list of dragonflies and damselflies is based on published records.
Odonata are thought to have arisen during the Carboniferous period (250 – 300 million years ago). Some of these ancient dragonflies were giants, with wingspans of up to 70 cm. Over time, the Odonata split into 2 major paths: the dragonflies (Anisoptera) with dissimilar fore and hind wings and the damselflies (Zygoptera) with similar fore and hind wings. Most Alberta forms came from the south after the glacial retreat about 10,000 years ago.
Most damselflies and some dragonflies (the Darners) have well-developed ovipositors and lay their eggs in the tissue of aquatic plants. The rest of the dragonflies do not have this ability and so lay their eggs on either the stems of plants or on the water surface.
In a week or more, the eggs hatch into aquatic larvae that may spend several years hunting along the bottom of the pond or stream. To capture food, the larvae have specialized mouthparts called a labium. They are able to shoot these mouthparts out at high speed and, with hooks at the end, capture prey. They are opportunistic feeders and prey on insects, worms, tadpoles, snails, and even small minnows. The larvae grow until they are ready to emerge as adults. Rates of development depend on the amount of food and water temperature.
At emergence, the larvae leave the water and usually crawl up onto vegetation. There is no pupal stage. The larval skin splits and the adult emerges. The new adults need to pump their wings full of blood before they can fly and, during this period (up to several hours), they are highly susceptible to predation by birds, frogs, spiders and other dragonflies.
Once airborne, dragonflies are champions of insect flight. The wing design of the Odonata is more “primitive” than that of most other insects, having many veins and cells. However, it is very efficient and they use very little energy per unit of distance travelled.
We can use the wings to help tell the difference between dragonflies and the damselflies. Dragonflies always extend their wings away from their body. Damselflies usually fold their wings back along their body when not in use.
Adults need to spend time adjusting their body temperature. In the morning they bask in the sun and may shiver their flight muscles to generate enough heat to take off. When the sun gets too hot, they seek shade, take longer glides between wing beats, or increase the flow of blood to their thorax to help dissipate heat.
Odonates have very large eyes and more than 80 per cent of their brain is devoted to processing visual information. They have sharp visual acuity and the ability to see under low light levels. Their excellent eyesight is valuable both for hunting prey and avoiding predators.
Importance of Odonata
Odonates are ecologically important as both predators and prey. Amphibians, fish, birds and other aquatic invertebrates feed upon the larvae. One of their great benefits to us is the adults’ voracious appetite for pest insects such as mosquitoes, black flies, horse flies, aphids, and grasshoppers. Odonates are also possible indicators of water quality of wetlands. Besides, these insects are just beautiful and this has led to them being featured in various commercial products, such as jewellery and decorative items.
Dunkel, S. 2000. Dragonflies through Binoculars: A Field Guide to Dragonflies of North America. Oxford University Press,
Needham, J. G., M. J. Westfall, and M. L. May. 2000. Dragonflies of North America. Scientific Publishers, Gainesville, Florida.
Walker, E. 1953. The Odonata of Canada and Alaska. University of Toronto Press, Toronto.
Westfall, M. J., and M. L. May. 1999. Damselflies of North America. Scientific Publishers, Gainesville, Florida.
Photographs of most Athabasca dragonflies: http://www.ups.edu/biology/museum/
Information on Alberta dragonflies: http://www.ualberta.ca/staff/lfoote/research/dragonfly.htm
Drawings of larvae and damselfly adults from: Morgan, A. 1930. Field Book of Ponds and Streams. G. P. Putnam’s Sons, N.Y.
Drawings of adult dragonflies adapted from: Needham, J., et al. 2000. Dragonflies of North America. Scientific Publishers, Washington.
Tim Terry, Athabasca University, prepared this brochure for:
Science Outreach - Athabasca (http://scienceoutreach.ab.ca).
This pamphlet was sponsored by Crooked Creek Conservancy Society of Athabasca, with assistance provided by an Alberta Community Lottery Board grant.