What’s That Bug? Dragonflies

What’s That Bug? Dragonflies

Some Texas garden insects are impossible not to notice, either due to their appearance or because of their behavior. Dragonflies stand out for both reasons. What gardener hasn’t noticed a large colorful dragonfly conspicuously perched in the garden on a hot summer’s day? Or noticed dozens of them at dusk swooping around high in the sky as they hunt for mosquitoes? These remarkable insects, with common names such as petaltails, spiketails, cruisers, meadowhawks, baskettails, emeralds, skimmers, darners and clubtails, are extremely interesting and highly beneficial insects that every Texas gardener should appreciate.

Three-hundred-twenty-seven dragonfly species have been documented in North America, with 160 of those being found in Texas. They, plus their smaller cousins, the damselflies, belong to the insect order Odonata, derived from the Greek word odonto, which means tooth. Dragonflies are split off from damselflies into suborder Anisoptera. Most species live only a few weeks as adults, but some can live up to a year. The largest dragonfly found in Texas, with a wingspan of more than 5 inches, is the giant darner (Anax walsinghami), and the smallest is the little blue dragonlet (Erythrodiplax minuscula), with a wingspan not much more than 1.5 inches. Speaking of size, dragonflies have been around for a long time, more than 300 million years, and there are fossils of some that had a wingspan exceeding two feet!

Like all insects, dragonflies have three body segments; a head, thorax and abdomen. Attached to the thorax are three pairs of legs and two pairs of wings. The wings are net-veined and translucent, sometimes with colored patches that vary with species. When perched, the wings are held straight out at right-angles from the body. Each wing acts independently, and this is the reason why dragonflies are so nimble in flight. They can fly forward, backward, hover and make a hairpin turn with ease. Remarkably, some have been clocked at flying faster than 20 miles per hour!

Besides their extraordinary flying abilities, another noticeable physical characteristic of dragonflies is their enormous compound eyes that take up much of their head. Each eye has up to 30,000 facets, called ommatidia, which allows them to see nearly 360 degrees, with just one blind spot directly behind them. Along with their remarkable flying ability, they use this excellent eyesight when hunting prey, which consists of many flying insects (such as flies, gnats and even other dragonflies). Mosquitoes are high on their list of prey, and a single dragonfly can eat hundreds of them per day.

Besides prey capture, male dragonflies spend a lot of their time competing for territory. Their aerial battles are easily observed, especially along the banks of any body of water. Males are also on the lookout for females to mate with. When he spots a female, a male approaches her and, with special claspers on the tip of his abdomen, he grasps her on the back of her neck. The male straightens out his body and they fly around in this position known as tandem linkage. After a bit, the female will curl her abdomen forward to connect with the male. This mating position is called the wheel.

Once mated, the female is ready to lay eggs. This must take place in or near a source of water, and each species has different requirements. Some prefer calm water, such as ponds or lakes. Others prefer clean running streams. Some species will dive underwater and lay their eggs on vegetation. Others may only dip their abdomens into the water, whereas some will cast their eggs out while flying above the water’s surface. In some species, the male will guard the female while she lays eggs. The eggs will then hatch in one to eight weeks, depending on species.

Dragonflies go through an incomplete metamorphosis. So instead of a caterpillar stage, they hatch out in a larval stage called the naiad. In this stage, they live underwater for up to two years, preying upon other aquatic insects and sometimes larger prey (such as minnows and tadpoles, even other naiads). As they grow, they will periodically molt (some species up to 17 times). For their final molt into adulthood, naiads will crawl out of the water, usually at night and under the cover of darkness. They’ll climb up onto a suitable surface, such as a cattail, twig or boat dock.

Then the top of the thorax splits and the new adult pulls itself out. Its wings will pump with fluids, expand and harden. This process takes a few hours, and at this stage these insects are vulnerable to predators such as ants or birds. Once the new exoskeleton hardens, the dragonfly takes flight. At this stage (known as a teneral), the young adult is still not mature, and it will still take a couple of weeks for its exoskeleton to fully harden and obtain its full adult coloring. Then, the dragonfly starts the cycle all over again.

Dragonflies are common near water and are excellent indicators of the quality of habitat. Some species, however, wander far from wetlands and some actually migrate. A few species are crepuscular (active at dusk), but most are diurnal (active during the day). One interesting behavior is when they thermal-regulate during the heat of the day. To reduce overheating, some species will point their abdomen up directly at the sun. This reduces the surface area exposed to the sun’s rays and keeps them from overheating. This ‘head-standing’ pose is called the obelisk position. Some species will also angle their wings downward to reduce exposure to sunlight. All of these poses make for some interesting behavior to observe.

Observing dragonflies is easy and has become a popular hobby. Besides watching for them in a Texas garden, the best place is to look for them is along bodies of water. Lakes, creeks, rivers and ponds will all have many species. Prairies, edges of woods and even deserts will have some. Being mostly large insects, dragonflies are easy to watch without any special equipment, but if one is serious, a pair of close-focusing binoculars and a good field guide are appropriate tools to have. A wonderful book covering our state is Dragonflies of Texas: A Field Guide by John Abbott. Texas gardeners and citizen scientists can also contribute to knowledge about these remarkable creatures by reporting sightings to the website Odonata Central at www.odonatacentral.org (maintained by John Abbott).

Dragonflies are remarkable insects. Amazing aerial acrobatics and colorful winged bodies make them a joy to observe. Combine that beauty and grace with a ravenous appetite for mosquitos and you quickly understand why these ancient creatures are some of the most beloved insects in both Texas and the world.