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Dragonflies: Water Garden Gems

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Oh, my aching muscles...

dragonflyweb.jpg

By Mary Gutierrez

People fall into two camps: those who like dragonflies, and those who think they are creepy. My husband gets the willies when he sees them, whereas I think they look like jewels flitting over the water. Regardless of your feelings toward these lacy-winged creatures, be glad you weren't roaming the earth 250 million years ago. Dragonfly fossils from the era have a wingspan of over two feet.

Dragonflies of various scientific denominations are also commonly called darners, damselflies, clubtails and skimmers. For convenience, I'm calling them all dragonflies! If you're interested in more detail about the order Odonata (which means "toothed jaw"), see the reading list that accompanies this story.

It's not necessary to know the order, family, genus and species of  each dragonfly. What is most important for the water gardener to know about dragonflies is the relationship that these insects have with the pond. Some pondkeepers believe that dragonflies are pests; others are starting to view their symbiotic relationship with water gardens as a beneficial one. One thing is for certain, though.  The presence of dragonflies around your pond is an indication of the health and diversity of your water garden's ecosystem.

The Invisible Dragonfly

The reason you see dragonflies around bodies of water is that they spend the majority of their lives as aquatic creatures. Their entire life cycle, from egg to death, can last from one to over five years, depending on the species. Dragonflies are on the wing for only a fraction of their lives.

Female dragonflies lay their eggs in aquatic vegetation, mud or in open water in ponds, lakes and rivers. Eggs hatch into nymphs, called naiads, when conditions are right, usually within a few weeks or months. Like other insects, dragonfly larvae spend their time feeding, molting their skin in a series of "instars," preparing to become adults.

I've read some water gardening authors who describe the "hideousness" of dragonfly larvae. One author describes them as "scorpion-like creatures" that wait in the mud for prey. They breathe with gills, occasionally shooting out their claw-like lower jaw (called a "mask") to impale a snack. Their large google-eyes are retained into adulthood.

The advocates of the "dragonflies are pests" theory have correctly observed one trait of dragonfly larvae:  they will eat just about anything that is smaller than they are. Dragonfly larvae are predators of small fry and tadpoles-those creatures that we want in our ponds. It can be heartbreaking to find that most of your newly-hatched goldfish or koi have disappeared without a trace.

To their credit, dragonfly larvae consume some pond pests, too. They munch on mosquito larvae, leeches, bloodworms, snails and other bugs. The dragonfly larvae are, in turn, eaten by adult fish, frogs, and birds.

Eventually, dragonfly larvae metamorphize into adults. The larvae crawl up on a reed or a stem and attach themselves firmly. Soon, their hardened skin breaks open and the adult dragonfly struggles forth. Body fluids are vigorously pumped throughout the insect's body, causing the body and wing buds to expand. The wing buds then unfurl into the lacy wings that will carry the dragonfly through adulthood.

To complete the life cycle, dragonflies head away from the water. Within days, they have developed their full coloring and sexual maturity. Like the larvae, adult dragonflies are voracious feeders. Here's where they truly become an important beneficial insect. They consume large quantities of flies, mosquitoes and other flying insect pests.

Dragonfly are--at worst--just a part of the water garden's food chain. If the pond ecosystem is out of balance, for example, with too many dragonfly larvae, not enough plants, and few other insects, the larvae will decimate young fish populations. It is important to maintain a good balance of all they key players in the pond. The water gardener can encourage a healthy pond ecosystem that supports all of the flora and fauna by not using pesticides anywhere in the garden.

Dragonfly trivia

Dragonflies have three small eyes on the top of their head that have nerves directly connected to the wings muscles. These eyes track the horizon and continually adjust the dragonfly's orientation in flight.

Dragonflies can fly forwards, backwards and sideways. They can also hover.

Dragonflies can glide to conserve energy on long flights. Some cross the Pacific Ocean.

The dragonfly's legs are held in front of their head and are used to scoop up insects which are devoured in flight. They are unable to walk-just perch.

Some dragonfly larvae breathe using gills located inside their abdomen. They suck water into the abdomen, passing it over the gills. They can also expel the water rapidly, giving them "jet propulsion" to move through water.

Male dragonflies are territorial. While waiting for females, they will chase off other males that enter their territory. Some species "time share." A male will occupy a territory for 20 minutes or so, and then move on to feed, allowing another male to use the territory for a short period.

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