The Dragonfly Air-Defense System
The afternoon had been advertised as peaceful.
The pond lay bright and still between the firs. Cattails leaned gently over the shallows, wildflowers crowded the bank and the mountains reflected perfectly in the water. Otto had selected a comfortable log, opened his field notes and prepared to spend several uninterrupted hours observing nature.
Echo had come because Otto mentioned snacks.
“I was promised a peaceful afternoon,” Otto said.
Echo looked out over the water, where the air above the reeds was already beginning to shimmer with very small things.
“You were misinformed.”
Today’s Special
The mosquitoes found Otto within minutes.
He waved one paw beside his ear. This accomplished nothing, so he waved both paws, which accomplished the same thing with considerably more effort.
“They’re everywhere!”
Echo remained perfectly still.
“Apparently, you’re today’s special.”
Mosquitoes locate potential hosts using a combination of signals. Carbon dioxide from breath can alert them that an animal is nearby. As they approach, body heat, moisture and skin odors help guide them toward a landing place.
Otto was broadcasting several of those signals at once.
Echo, meanwhile, watched from his branch with the relaxed confidence of someone who was not currently the preferred item on the menu.
Then something blue flashed across the pond.
A mosquito that had been following an otherwise ordinary flight path abruptly vanished from the afternoon.
Otto froze.
“Did you see that?”
The dragonfly banked over the cattails and continued along the shoreline.
“Efficient,” Echo said.
Solving the Interception
Calling a dragonfly efficient is something of an understatement.
A dragonfly does not always need to follow directly behind its prey. It can watch an insect’s movement and steer toward a point where the two flight paths will meet. Instead of aiming only at where its target is now, it adjusts for where the target is going.
The basic geometry resembles the strategy used by an outfielder moving beneath a fly ball: keep the target in a consistent part of the visual field while closing the distance. If the angle remains steady and the gap continues shrinking, predator and prey are headed toward the same place.
For the mosquito, this arrangement ends badly.
For the dragonfly, it frequently ends with lunch.
The entire interception may happen so quickly that it appears less like a chase and more like the mosquito has been edited out of the landscape.
Otto pointed with his whole arm.
“Dragonflies catch their prey in midair!”
Echo watched another one cross the pond.
He had already covered this under “efficient,” but Otto was taking notes now, and there was no stopping the lecture once the notebook came out.
Built for the Job
A dragonfly’s head is dominated by two enormous compound eyes made up of thousands of individual visual units. Together, they provide an exceptionally broad view of the surrounding airspace and help the dragonfly detect small moving targets against the sky.
That becomes especially important when the air is crowded.
To us, a cloud of midges may look like a single shifting blur. A dragonfly can concentrate on one potential target and continue tracking it even as other insects pass nearby. Its nervous system filters an entire sky full of movement down to one very unfortunate dot.
The wings provide the maneuverability needed to reach it.
Dragonflies have four wings controlled with remarkable precision. By altering their timing and angle, a dragonfly can accelerate rapidly, hover, glide, make sharp turns and even fly backward. The result is an aircraft capable of changing direction far faster than Otto could point at it.
The final piece of equipment is underneath.
During an interception, the dragonfly holds its six bristled legs forward, forming a basket. When it reaches its prey, the insect is scooped from the air and held securely. Some dragonflies begin eating before they have even bothered to land.
Otto lowered his binoculars.
“The pond has its own air-defense system.”
Manufactured on Site
The most impressive part of the system is not what happens above the pond.
It is what has already happened beneath it.
Dragonflies begin life underwater as aquatic nymphs. Depending on the species and conditions, they may spend months or several years prowling among submerged plants, stones and debris before becoming the winged adults we recognize.
The nymph is a predator too.
Its lower lip is modified into a hinged grasping structure that rests folded beneath its head. When prey comes within range, an elastic, spring-loaded mechanism launches this apparatus forward with startling speed. The extended mouthpart grabs the target and pulls it back toward the nymph.
Mosquito larvae, aquatic insects, small crustaceans and other pond animals may all become part of its diet. Larger dragonfly nymphs can occasionally capture tadpoles or very small fish.
They have another unusual piece of equipment as well. Dragonfly nymphs draw water into a chamber containing internal gills. If one needs to escape quickly, it can force that water back out and propel itself away like a tiny aquatic rocket.
The pond does not simply attract its summer patrol.
It grows it.
When a nymph is ready to become an adult, it climbs out of the water on a plant stem, rock or log. Its outer skin splits, and the adult slowly pulls itself free. Its soft wings expand, harden and eventually carry it over the same water where it spent the earlier part of its life.
The empty nymph skin—called an exuvia—may remain attached near the shoreline long after the dragonfly has departed.
Otto added an underwater level to his security diagram.
“Defense above and below the surface,” he said. “Very thorough.”
Mostly Secure
As the afternoon continued, Otto began recognizing different patrol styles.
Some dragonflies cruised continuously over the water, following repeated paths along the shoreline. Others selected a favorite twig or reed, waited for something edible to pass and then launched before returning to nearly the same perch.
A few chased other dragonflies away from particularly desirable territories.
To Otto, the organization appeared flawless.
“Our patrol area is officially secure.”
Echo glanced at the mosquitoes still circling Otto’s head.
“Mostly.”
That qualification mattered.
Dragonflies eat mosquitoes, but they are not specialized mosquito-control agents. They are generalist predators that also capture midges, flies, gnats, mayflies, moths and sometimes other dragonflies. Mosquitoes are part of the menu, not the entire mission.
Even a pond filled with dragonflies will still have mosquitoes. No aerial patrol catches everything, and no healthy ecosystem is built around making one naturalist completely comfortable.
Mosquitoes and other small insects are also part of the food web. They feed fish, frogs, birds, bats and countless predatory insects. The pond is not divided neatly into helpful creatures and annoying ones. It is a shifting collection of appetites, ambushes and narrow escapes.
Sometimes the dragonfly wins.
Sometimes the mosquito wins.
Sometimes Otto discovers that he is standing in the middle of the contest.
One Hostile Approaching
Late in the afternoon, Echo produced a clipboard.
Otto did not remember packing a clipboard, but Echo had already begun conducting a formal security assessment.
“One hostile approaching the snack perimeter,” Echo announced.
A mosquito drifted toward the log.
The nearest dragonfly changed direction, accelerated across the shallows and intercepted it just above the water. A moment later, the dragonfly hovered near Echo’s branch, close enough for them to see its immense eyes and folded basket of spiny legs.
Echo studied it carefully.
“Ask whether it accepts payment in crumbs.”
It did not.
The dragonfly was not actually defending the snacks. It had no opinion about Otto, Echo or the security of their picnic. It was simply hunting in a place where hunting happened to benefit everyone sitting on that particular log.
That did not make it any less deserving of appreciation.
A forest community is full of creatures pursuing their own lives in ways that quietly support others. Trees cool the shoreline. Wetland plants shelter young animals and hold the soil in place. Aquatic insects feed the birds. Dragonflies collect some of the mosquitoes before they reach Otto’s ears.
None of them attended a planning meeting.
They are still part of the same system.
Field Notes from the Pond
To observe your local dragonfly patrol, visit a pond, marsh, lake or slow-moving stream on a warm, sunny day. Watch the open air above the water and the vegetation along the shoreline.
You may see dragonflies:
- Patrolling the same stretch of water repeatedly
- Hovering briefly before making a sudden turn
- Launching from a favorite twig and returning to it
- Chasing rivals away from a territory
- Catching small insects in flight
- Dipping toward the water or vegetation to lay eggs
- Resting with their wings spread outward
You may also encounter damselflies, their generally smaller and more delicate relatives. Most dragonflies rest with their wings held open, while many damselflies fold their wings together over their bodies. Dragonfly eyes also tend to be much larger and closer together, while damselfly eyes are usually separated across the head.
Look closely at stems, logs and rocks near the waterline. If the pond is producing dragonflies, you may find the empty, split-backed skins left behind when the adults emerged.
The best way to support them is to protect the water that produces them. Healthy shoreline vegetation, places for nymphs to climb out, stable aquatic habitat and freedom from unnecessary pesticide runoff matter far more than anything we could install above the pond.
The air-defense system begins underwater.
End of Patrol
As the light grew warmer, Otto closed his field notes.
Dragonflies continued sweeping over the cattails, banking through clouds of insects and returning to their perches. The pond looked as peaceful as it had when Otto arrived, although he now understood how much work was required to make it look that way.
One last blue-green hunter passed over the log.
Echo raised his mug toward it in acknowledgment.
The dragonfly did not accept crumbs, request praise or file a patrol report.
It simply turned back toward the water and continued its shift.
Summer security, after all, is a team effort.