DragonFly habits

After yesteray’s dragonfly piece Missouri reader Jim Griffin sent us some fact about dragonflies in the Ozarks, remarking he used to write a newspaper “Nature Notes” column. Thanks Jim interesting stuff

Living near water most of their lives, dragonflies are both useful and beautiful. These long, slim-bodied insects come in a wide variety of vivid colors including blue, green, red, purple, and even bronze. Their wings seem to shimmer as if made of silver. They have been around for a long time. Dragonfly fossils with wingspans exceeding twenty-seven inches have been found dating back over two hundred million years, predating the dinosaurs. Today there are over four hundred individual species in North America with the largest having a wingspan of six inches.

In our area, most dragonflies are an inch or two long with wingspans up to three inches. They actually have two separate sets of wings that can be moved in different directions at the same time. This enables them to travel at speeds up to sixty miles per hour and then stop, hover, turn around in mid-air, fly backward, and even land in an instant. Dragonflies beat their wings while in flight twenty to thirty times per second. They depend on their eyes for hunting and can focus on objects twenty feet away. Their eyes are enormous and are divided in half circles. One half looks up for danger while the other half looks down for prey. Each compound eye contains about twenty-eight thousand lenses. Their specialized vision is superior to any other insect.

Because of their voracious appetite, dragonflies spend most of their time hunting for food. They form a basket with their spiny legs to scoop up insects and eat them in flight. Other than catching insects, dragonflies can only use their legs to cling to objects such as twigs while resting. Dragonflies cannot walk. Most hunt during the day, but a few are crepuscular (evening) hunters. They often hunt in groups when suitable prey is abundant. They love mosquitoes and have been nicknamed “mosquito hawk”. One dragonfly can consume over six hundred mosquitoes in a day. Although dragonflies were originally named due to their dragon-like jaws, they pose no threat to humans. They neither sting nor bite and are completely harmless.

Surprisingly, dragonflies spend only a short part of their lives in the form most familiar to us. After mating, females lay thousands of eggs in or near the water. It takes from a few days to several months for the eggs to hatch into dingy brown nymphs called naiads. These naiads have six walking legs and live underwater hiding beneath stones and debris. They breathe through gills located inside their abdomen. Their favorite foods are tadpoles, small fish, mosquito larvae, water bugs, and other dragonfly nymphs. They choose to wait in ambush rather than chase their prey. The naiads can go several weeks between meals.

As the naiads grow, their skin is molted up to fifteen times. One evening after a period of up to five years, the naiads crawl from the water and attach themselves to twigs or weed stems. They go through one final molt and this time mature dragonflies emerge. After another four hours they stretch out their wings and blood starts to pump into them making them stiff and strong. The sun dries and hardens their wings and bodies, but it takes up to an additional month before they reach maximum color.

Mature dragonflies spend much of their time away from water. This period ranges from a few days to a couple of weeks, but can be longer in species that migrate. Little is know about why dragonflies migrate although the movement of massive swarms is well documented in North America. Speculation is that drought may be a factor. Adults live only about three months, so these migrations are intergenerational movements in which one generation carries out the migration in one direction with its offspring making the return trip. Dragonflies are believed to navigate by observing the position of the sun in the sky. An internal “clock” automatically compensates for the earth’s rotation and keeps them on course.

Dragonflies are studied by ecologists to determine changes in the environment due to their position at the top of the insect food chain during all stages of their life. The presence of dragonflies not only keeps the population of unwanted insects such as mosquitoes in check but also indicates a healthy overall ecosystem.

Jim Griffin

Cape Girardeau, MO