Monday, June 29, 2015

Flame Skimmer 

Bugs bigger than birds might sound scary, but most folks agree that dragonflies are more mesmerizing than fearsome. One of our local dragonflies, the Giant Darner, is the largest dragonfly in North America, with a five inch wingspan, and an equally long body. That's just a tad larger than the wingspan of some of our common hummingbirds! Although they are carnivorous, there's no need to worry: dragonflies don't sting or bite humans, but feast on bugs that do annoy us, like mosquitoes and gnats.

Since these fascinating insects are in the taxonomic order Odonata, the sport of dragonfly watching is called "oding." If you are beginner in the sport, you may just want to learn the difference between two major groups, or suborders, the damselflies (Zygoptera) and the dragonflies (Anisoptera), which can be distinguished at a glance. Dragonflies hold their wings horizontally at rest; the more slender damselflies fold their wings over their back when perched.
Powdered Dancer

Dragonflies and damselflies were not granted official common names until 1996. Before that, they were known mostly by their Latin family or species name; at least two dozen families and more than 5,500 species are currently recognized world-wide. A dozen or so species are commonly seen around suburban Phoenix, and more than a hundred are known throughout Arizona.

None of them can walk, but all are exceptional fliers, able to cruise at about 10 mph on average, and put o 30 mph, beating their wings at thirty times per second. They can move in any direction as well as hover, inspiring aeronautical engineers to study them in detail for clues to better mechanical design.

However, it is the monstrous looking aquatic larval stage that earned the group the common name "dragon" and the Latin name, Odonata, which means "toothed," for an over sized spiny jaw that extends like an arm to grab prey. Dragonfly larvae, also known as nymphs, live in freshwater ponds and streams where they hunt other insects, tadpoles and small fish. You can easily spot a damselfly nymph by the three feathery looking gills at the tip of their abdomen or "tail" and by the way they wiggle their body as they swim through water. The gills of dragonfly nymphs, in contrast, are inside their body. They move in quick bursts by squirting water out the end of their abdomen like miniature underwater jet boats.
Exuvia or husk of larva 

When a larva is ready to transform into an adult, it crawls out of the water, cracks open its skin right down the middle of its back, and slowly crawls out to begin a few weeks or months of life on the wing. In most species, males and females look very different, and like birds, the males are usually more brightly colored than the females. Male dragonflies are also territorial, and will chase off other males that intrude on their favorite stretch of stream or shoreline, but welcome females. Once he does find a mate, he latches onto her neck with special claws at the tip of his abdomen. The pair mate in flight, making a "heart" or "wheel" shape with their long abdomens. He will continue to guard her so that she can't mate with other males.

To complete the life cycle, a female will lay between 500-2000 eggs. If you see a dragonfly dipping the tip of its abdomen on the water while in flight, it is a female laying her eggs, one by one. Damselflies lay their eggs in the stems of plants where the hatched larvae can easily crawl into the water. Nymphs live under water between one and five years before emerging in their full glory as winged dragons and damsels. Hot summer days are the best time to spot dragonflies cruising desert washes and urban ponds where they patrol for meals and mates, so now is the time to get out your binoculars and do some doing!

Learn more about local dragonflies at a website created by ASU professor Pierre Deviche and dedicated to Arizona dragonflies.

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