Jewels of the Riverbank
By Awake! correspondent in Spain
WHENEVER I stroll alongside a river or a pond, I invariably search for one of my favorite jewels—it may be red, blue, or green. I sometimes spot one lying motionlessly on a leaf; I may see another hovering over the water or even darting in front of me. The jewel I seek is the dragonfly—the flashy “helicopter” of the insect world.
These flying gems first caught my attention many years ago when I stumbled upon a lazy stream running through the woods. Flitting in and out of the sunlight were several dragonflies—some a bright metallic blue and others a resplendent greenish-yellow. I spent an hour observing their aerial dances, which transformed the forest glade into a miniature ballroom. They have intrigued me ever since.
The more I learned about dragonflies, the more I came to appreciate their beauty and their worth. My first discovery was that there is a difference between dragonflies and damselflies. The dragonflies are powerful fliers and are usually larger, whereas the damselflies—as their name implies—are daintier, with a much more timid flight. A principal difference has to do with the way they hold their wings. A dragonfly at rest usually holds out both pairs of wings horizontally, while a damselfly folds them together above its body.*
I began to wonder how dragonflies can pluck mosquitoes out of the air with such apparent ease. Personally, I find it almost impossible to swat a large fly that is basking on the kitchen wall. ‘What,’ I asked myself, ‘has a dragonfly got that I haven’t?’ Two things: total mastery of the air and eyes that would make a watchman turn green with envy.
The Flight of the Dragonfly
To call a dragonfly a helicopter—a common nickname in Spain—is really a disparaging analogy. Their aerial acrobatics are so fast that it is sometimes impossible for the eye to follow them. In short bursts, some species can reach a top speed of up to 60 miles [96 km] an hour. They can also hover or fly backward, forward, or sideways at a moment’s notice. Furthermore, when a dragonfly makes a tight turn in the air, scientists calculate, it must withstand a force of up to 2.5 G’s.
Dragonflies have two pairs of flexible, lacelike wings. Although these wings look delicate, they can beat up to 40 times a second and take knocks with a minimal amount of damage. Biologist Robin J. Wootton describes them as “small masterpieces of ingenious design.”
“The better we understand the functioning of insect wings,” he adds, “the more subtle and beautiful their designs appear. . . . They have few if any technological parallels.” Not surprisingly, the dragonfly’s flight techniques are currently being studied by aeronautical engineers.
A Head Full of Eyes
If the flight of the dragonfly is extraordinary, no less can be said of its eyesight. Two huge compound eyes almost cover the dragonfly’s head. Each of these eyes has up to 30,000 hexagonal units that are like tiny eyes within an eye, since each one transmits a separate image to the brain. That doesn’t mean, however, that a dragonfly sees thousands of different pictures, all at the same time. Rather than seeing a complete picture, as we do, it senses movement, patterns, contrasts, and shapes.
All those images need analyzing. Thus, 80 percent of a dragonfly’s brain is dedicated to assessing visual information. Few optical systems are as sensitive—a dragonfly can spot a mosquito some 60 feet [20 meters] away. Even at dusk, when the light is so dim that a human observer can barely spot tiny flies, tropical dragonflies easily capture them.
A dragonfly’s rapid, darting flight through riverside vegetation requires hundreds of split-second decisions. It can handle this formidable task because it can see up to a hundred distinct images a second, over five times more than we can. Thus, a movie, which projects 24 images a second, would just look like a series of still photos to a dragonfly.
A Change of Life-Style
When a dragonfly starts its life, there is no indication of the glossy highflier it will eventually become. After hatching, the aquatic larva stays more or less motionless in a pond or a stream, waiting to grab whatever food comes within reach. Many changes of skin later—several months or even years in the case of some species—the larva climbs out onto a reed. There, an extraordinary metamorphosis occurs.
The skin splits open along the thorax, and a fully formed dragonfly crawls out. Like a butterfly, the newly emerged adult has to wait a few hours before its wings become rigid and a new life begins. In a matter of days, its instinctive wisdom enables it to hunt successfully and master the intricacies of flight.
Soon the young dragonfly becomes an expert at catching flies and mosquitoes on the wing. Devouring its own weight in insects each day, it performs an invaluable service. To ensure a reliable food supply, many male dragonflies stake claims to small territories, which they jealously patrol.
Some species of dragonflies hunt aphids or beetles, others capture tiny frogs, and one tropical damselfly even feeds on spiders. It hovers around the web of a large orb-spider and grabs the smaller spiders that visit the web to scavenge food morsels that the web’s owner leaves behind.
Evidence Against Evolution
Many evolutionary scientists consider dragonflies to be the earliest flying insects. One fossil discovered in France is the impression of wings of a dragonfly that had a wingspan of two and a half feet [75 cm]! It is the largest insect known, being more than three times the size of any living dragonfly.
‘How would it be possible,’ I asked myself, ‘for one of the most complex flight mechanisms known to man to simply appear, perfectly developed?’ “There are no fossils of insects which are intermediate between the wingless and winged state,” admits the book Alien Empire—An Exploration of the Lives of Insects. It is evident that dragonflies are the handiwork of an intelligent Master Designer.
Dragonflies have successfully colonized almost every part of the globe. They will make themselves at home alongside an alpine lake, an equatorial swamp, or even a suburban swimming pool.
I have watched swarms of dragonflies on a tropical beach in Africa as well as lone emperor dragonflies relentlessly patrolling their favorite European pond. And when I traveled by canoe through a leafy canyon in the Philippines, brilliant damselflies served as an escort, even alighting on my bare arms.
While dragonflies may be among the most sophisticated flying machines on earth, I have always been more impressed by their grace and beauty than by their flying abilities. Their presence adds a special sparkle to our ponds and riverbanks. They are the ideal jewels—always there to be enjoyed.
Occasionally, dragonflies angle their wings downward and point their body upward toward the sun. This is a posture they adopt to cool down, since it minimizes the body area exposed to the sun.
[Pictures on page 16, 17]
Dragonflies, which rest their wings horizontally, are usually larger than damselflies, which fold their wings above their bodies