Human activity imperils one of the Earth’s great survivalists: dragonflies
Sixty-six million years ago, a giant rock streaked through the cosmos and crashed into Earth, causing fires that covered the land and creating soot that blocked out the sun for at least a year. The asteroid’s impact wiped out dinosaurs and 75 percent of all other animal groups, yet dragonflies survived.
About 50 million years ago, the Earth witnessed the boom of a feathery new super-predator that patrolled the skies and outmaneuvered most aerial creatures before it. Birds became perhaps the most formidable enemy of winged insects and other flying creatures — and yet dragonflies survived.
Today, industrial human societies are disrupting the Earth’s ecosystems on many fronts by warming the planet’s climate, clear-cutting its once-abundant forests and draining its ageless lakes and streams. Despite surviving the impacts of asteroids, the arrival of arch nemeses and the insults of myriad other threats, it is no sure bet that dragonflies will survive this time.
Dragonflies are among the Earth’s oldest existing groups of animals. Based on exceptionally preserved fossil specimens, our best estimate is that the ancestor of modern-day dragonflies originated more than 200 million years ago. Some pre-historic dragonfly ancestors were quite large, but, for the most part, fossils indicate that ancient dragonflies and their relatives looked fairly similar to what we have today. This means that dragonflies have been around in their current form since before iconic dinosaurs like Tyrannosaurus or Triceratops roamed the Earth, since before the continent of North America broke off from Eurasia and since before flowers first bloomed.
You may or may not spend much time considering the dragonflies that you see today, but I imagine you can appreciate their impressive record of survival through the ages. Given this remarkable run of stability, it is ominous for the rest of us animals that there are warning signs that dragonflies may now be in some trouble.
The decimation of 35 percent of the world’s wetlands through over-use and global warming threatens many dragonflies — a group of animals that withstood a worldwide drought so severe that the tropics received less rain than the Sahara Desert does today. Dragonflies, like frogs, spend their juvenile stage developing in the water and then undergo a metamorphosis. With lakes and streams currently drying and draining, dragonflies have fewer places to live than they did even a hundred years ago. After 200 million years of developing in the water, it is quite unlikely that they will suddenly learn to develop on land, which makes the drying and destruction of wetlands perhaps the most serious threat facing dragonflies today.
Even among the waterbodies that have not yet disappeared completely, shallower lakes and more stagnant streams allow for lower concentrations of the dissolved oxygen that juvenile dragonflies need to breathe. As a result, some remaining waterbodies are now poorly suited for the growth and survival of many dragonfly species.
The influx of novel chemicals into our waterways also endangers many dragonflies — a group of animals that survived global storms of acid rain that made water bodies uninhabitable to many other organisms. Pesticides like carbaryl and malathion are used to control pests like ticks and fruit flies, but these chemicals are often encountered by dragonflies after they runoff into streams and lakes. Researchers have shown that dragonflies die when exposed to pesticide concentrations that can be found in many waterbodies. High levels of metals and man-made pollutants also accumulate in the ponds and wetlands that are constructed near highways. Although dragonflies often inhabit these highway-adjacent wetlands, the chemicals that accumulate in these ponds can damage the dragonflies’ DNA molecules, rendering them extremely susceptible to harmful mutations and the degeneration of their bodies’ cells.
The heating of our atmosphere further imperils many dragonflies — a group of animals that lived through countless ice ages and a decade-plus winter of perpetual subfreezing conditions. Tropical dragonflies have always lived near the limits of their heat tolerance, but rapid warming is now placing many such species at risk of exceeding those limits and facing extinction.
Additionally, numerous dragonfly species display dark patches of melanin on their wings to attract mates and intimidate rivals, but the solar radiation absorbed by these patches can cause dragonflies to overheat in warm parts of the globe. My recent research with colleagues shows that dragonflies will need to substantially shrink or eliminate these patches in order to survive in the warmer climates of next century. We do not yet know if dragonflies will be able to make these changes fast enough to match rising global temperatures. Even if dragonflies can keep pace, the rapid loss of these traits could disrupt their ability to successfully mate and perpetuate themselves
Many of you likely have heard scientists raise alarms before. I suspect that everyone can sense that something’s wrong: It’s warmer than it used to be; there’s less water and more wildfires than there used to be; there are more chemicals in the drinking water than there used to be. The research in dragonflies underscores that these environmental changes are not trivial and that animals may not just simply adjust. Human degradation of the environment is becoming harmful enough to organic life that it could imperil animals that have managed to survive one global apocalypse after another. Do we really want to be responsible for that kind of devastation? Do we really want future generations to consider us more destructive than an asteroid?
We still have time to implement policies that pull us back from the brink, but the window is closing. Without action, we will be remembered for debasing the environment so badly that it finally altered or eradicated even the toughest creatures in Earth’s history.
Michael P. Moore, Ph.D., is a biodiversity post-doctoral fellow with the Living Earth Collaborative and Washington University in St. Louis. His research focuses on the evolution of life cycles and mating strategies in insects and amphibians. Follow him on Twitter: @moore_evo_eco