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Going 'oding' for dragonflies

Posted: August 30, 2012 - 3:28pm  |  Updated: August 31, 2012 - 8:17am
Sedge darners (male above, female below) in the "wheel position" on a wire fence. This is one of 13 dragonfly species on the Kenai National Wildlife Refuge.  John Morton
John Morton
Sedge darners (male above, female below) in the "wheel position" on a wire fence. This is one of 13 dragonfly species on the Kenai National Wildlife Refuge.

In exchange for ice cream, my 10-year old daughter, Charly, and her friend, Anya, were picking currants when a couple of sedge darners landed nearby. Once the girls figured out that the dragonflies were mating, they changed their tune from “cool” to “gross” pretty quickly. The dragonflies were locked in the “wheel position” that looks a lot like a heart (see photo). This got me to wondering why these insects were having sex so late in the summer.

As it turns out, this is a normal part of the dragonfly lifecycle. Adults live only 1 to 2 months, and summers are short in Alaska after dragonflies emerge in the spring. Prior to their brief time as winged adults, they may spend as much as six years as larvae (also called nymphs) at the bottom of a lake, stream or wetland. During this time, they may molt 8 to 17 times, with their developing wingbuds getting larger each time. Some species overwinter as eggs and some as nymphs.

Dragonflies and damselflies belong to the insect order, Odonata, which is Greek for “toothed jaws.” Even as larvae, dragonflies have an enormous hinged labium, a lower lip with pincers that can be extended to catch small aquatic insects, crustaceans and even fish and tadpoles. Dr. Mari Reeves and her colleagues published an article last year that attributed the high rate of skeletal abnormalities in wood frogs on the Kenai National Wildlife Refuge mostly to severed limbs that result from failed predation of tadpoles by dragonfly nymphs.

As everyone knows, dragonflies can move. Their four wings can operate independently, allowing them to fly upwards, sideways, backwards and forwards. Large darners fly up to 40 mph and, unofficially, have been clocked at 60 mph. But not all Odonates fly all of the time. Darners, emeralds, spiketails, river cruisers, and some skimmers are called “flyers” because they spend most of their active life flying. Damselflies, clubtails, and most skimmers are “perchers” because they spend much of their time doing exactly that.

Todd Sformo and Dr. Pat Doak, at the University of Alaska Fairbanks, studied the thermodynamic tradeoffs of these different strategies in 10 dragonfly species. Unlike humans and other homeotherms, dragonfly activity is mostly regulated by ambient temperature. However, dragonflies can bask in the sun (which is what most perchers do) or they can generate heat by flying, particularly using a technique called wing-whirring (which is what most flyers do). Additionally, different species have different minimum flight temperatures (MFTs), a physiological set point that is likely optimized for flight muscle enzymes. Sformo and Doak found that perchers have lower MFTs than fliers so they could operate for longer periods on cooler days. On the other hand, flyers tended to be larger species with more body mass and wing loading, so they could operate longer on warmer days.

Not only do dragonflies fly quickly, they fly far — in fact, the furthest of any known insect. A 2009 paper in the Journal of Tropical Ecology documents mass migration of millions of globe skimmers (and other dragonflies) from India to Africa, a 10,000-mile round-trip journey across the Indian Ocean that may take four generations to complete! Globe skimmers also fly high, recorded at over 20,000 feet in the Himalayas!

There are more than 30 Odonate species in Alaska. Thirteen species have been documented on the Refuge, the most recent species (the variable darner) identified just two weeks ago by Janine Ray, an observant seasonal employee. If you’re looking for a good place to search for dragonflies, Headquarters Lake off Ski Hill Road is as good as any. John Hudson, the author of “Dragonflies of Alaska,” identified eight species on this lake in 2010 including the sedge darner, lake darner, American emerald, ringed emerald, boreal bluet, northern bluet, four-spotted skimmer, and the red-waisted whiteface.

Chasing dragonflies is a lot like birding. Dragonfly fans call it “oding” (after Odonates), a new term that’s been finding traction on the Internet in recent years. Admittedly, it’s a little bit nerdy. In addition to “Dragonflies of Alaska,” “Dragonflies of British Columbia and the Yukon” by Robert A. Cannings is a good book to help with Odonate identification and life history.

Good oding!

 

John Morton is the supervisory biologist at Kenai National Wildlife Refuge. You can find more information about the refuge at http://kenai.fws.gov or http://www.facebook.com/kenainationalwildliferefuge.

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muir
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muir 09/08/12 - 05:59 am
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