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Chasing the dragonfly

Venture Out

Jim and Lynne Weber

With large, multifaceted eyes, two pairs of strong, transparent wings and an elongated body, the dragonfly is an ancient insect that inspires myth and lore in many cultures. For Native Americans, their form can represent swiftness and energy, pure water and even renewal after a time of great hardship.

Usually found around lakes, ponds streams and wetlands, dragonflies typically eat mosquitoes, midges and other small insects such as flies, bees and even some butterflies and other dragonflies. They capture their prey by clasping them with their spike-studded legs. Their prey cannot use their usual form of escape — diving away — because dragonflies are quite agile and are quick to attack from any angle. Dragonflies are harmless to humans and are considered beneficial, as they eat large numbers of flying insects. But their primary purpose in life is to reproduce.

The mating behavior of dragonflies is a multi-step process. The male has both a primary and secondary set of genitalia. He will first transfer sperm from the tip of his abdomen to the secondary structures on his second or third abdominal segment. Then, using the special structures at the tip of his abdomen, he will grab a receptive female by the back of her head. The pair is now considered to be in "tandem," and the male tows the female in flight. To complete the reproductive act, the female bends her abdomen beneath the male and touches the tip to the male's secondary structures. This position is called the copulation "wheel," and it is at this point that sperm is transferred to the female to fertilize her eggs.

The life cycle of a dragonfly consists of three stages: egg, larvae (or nymph) and adult. After mating, the female will lay her eggs on aquatic plants or deposit them in water. Once hatched, these nymphs begin their lives underwater, eating other aquatic creatures. Nymphs of larger dragonflies will even eat the nymphs of smaller species.

This nymphal stage can last as long as several years in some species, but most spend winter in ponds and marshes and emerge the next spring as adults. Once fully grown, the nymph will crawl out of the water onto a rock or up the stem of a plant, break through its skin (called the exuvia) and enlarge its body and wings by pumping fluids into them.

Mature dragonflies are known for their aerial acrobatics. They're capable of hovering and rapid acceleration and can both hunt and mate on the wing. They need to make the most of their time as aerial predators, because adults live only up to two months.

Adult dragonflies are often confused with damselflies, but they are two distinct insect suborders. Primarily, wing shape is the most diagnostic feature, with all four wings of damselflies being equal, while the hind wings of dragonflies are broader than the forewings. When at rest, damselflies hold their wings together and sometimes slightly above their body, whereas dragonflies hold their wings fully open horizontally or slightly down and forward. Additionally, the eyes on a damselfly are separated, while the eyes of many (but not all) dragonflies touch. Both damselflies and dragonflies are members of the scientific order Odonata, so their life cycles are very similar.

The common names for dragonfly species that occur in Texas are as colorful as the insects themselves — Autumn Meadowhawk (Sympetrum vicinum), Roseate Skimmer (Orthemis ferruginea), Eastern Pondhawk (Erythemis simplicicollis), Black Saddlebags (Tramea lacerata), Stream Cruiser (Didymops transversa), Halloween Pennant (Celithemis eponina) and Blue Dasher (Pachydiplax longipennis), to name a few. To some extent, the presence of dragonflies indicates ecosystem quality. Local populations and diversity may be strongly affected by changes in water flow, turbidity and types of aquatic or waterside vegetation. Not surprisingly, the greatest number of species is found at sites with natural water flows, high water quality, native plants and a variety of microhabitats.

When you see dragonflies this summer, admire their maneuverability, enjoy their jewel-like colors, appreciate their mosquito-eating, and be thankful that we no longer have the "giant dragonflies" from Jurassic and Cretaceous Periods — their wingspans were up to six times larger than those we have today.

Send your nature-related questions to naturewatch@austin.rr.com, and we'll do our best to answer them. If you enjoy reading these articles, look for our book, "Nature Watch Austin," published by Texas A&M University Press.

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