Insect Populations in Decline are Yet Another Invitation to Disaster

Scott Deshefy


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In the early 20th century, when asked if anything about “God” could be concluded from studying natural history, scientific polymath J.B.S. Haldane famously responded “he has an inordinate fondness for beetles.” Currently, more than 380,000 catalogued species of beetles in order Coleoptera make it the largest subset of the most species-rich and successful class of animals on Earth ─ insects. This may be the Anthropocene epoch because of our negative impacts on the planet, but an estimated 10 quintillion insects may inhabit the biosphere at any given time. In fact, however much it affronts our human arrogance, causing us to poison and genetically alter crops to combat their numbers we live in an Age of Insects. Theirs is not an invisible empire like that of bacteria and other diminutive organisms. Preceding even the great dinosaurs, they’ve colonized, adapted to and occupied nearly every ecological niche imaginable. Despite their meager dimensions, six-legged, segmented bodies have mastered the skies, freshwaters and soils, synchronizing multiple life cycle stages to seasonal abundances in plants and prey. So distinctively different are these stages, some insects breathe through spiracles as airborne adults, through gills as swimming larvae, and hunker down to metamorphose as pupae during hard times. Open oceans alone have been an impasse to their millions of species and huge, but fragmentary biomass. On oceanic swells, far from any shoreline, only the water strider Halobates can be found, searching for, as yet indeterminate prey. A “true bug,” like other Hemipterans gliding atop freshwater lakes and streams, it’s the only insect known with a seaward foothold.

Insects have been evolving on land and in ponds and other freshwater habitats for over 400 million years, burrowing and building (often elaborately), crawling, hopping, flying and swimming to survive, even living in terrestrial extremes. Stoneflies have been identified in the Himalayas at 18,000 feet and silverfish are found, not only in the damp recesses of our homes, but in caves 3,000 feet below the Earth’s surface. Alkali flies live in Yellowstone’s hot springs, while other insects survive freezing cold and arid conditions by aestivating, maintaining states of torpor for periods of months and even years. Feats of strength, ferocity and social organization among insects both awe and terrify us. In the darkness, a single gnat, flea or louse loosed about our beds, to paraphrase Lao Tzu, “is worse than a tiger.” Yet, we marvel at the migratory marathons of monarch butterflies, calculate the aerodynamic uncertainties of bumblebees in flight, and link our phobias to science fiction, creating giant insect menaces on screen. For centuries, as carriers of malaria and yellow fever, mosquitoes protected rainforests from human destruction. Now, due to global warming and climate change, dengue fever and other insect-borne diseases, once limited to the tropics, are gradually ranging north. In time, the world’s most venomous moth caterpillar, Lonomia oblique, which lives in New World subtropical jungles and can be deadly to humans, could arrive at America’s doorsteps.  Invasive species such as fire ants, gypsy moths, Asian hornets, and “killer bees” already have. But only begrudgingly are insects given their due. Instead, we’ve genetically modified our crops, bioengineered bacillus insecticides and upped the ante of toxic dusts to cope with insect resistances. Now, that’s coming home to roost.

For two weeks in August 1994 and again in August 2016, entomologists in Krefeld, Germany collected flying insects in identical traps at the same site. Similar studies in Germany were conducted at 63 protected areas over equivalent time spans. The shocking results: insect biomass had dropped 76 percent. Considering insects comprise an estimated 80 percent of all the animals known, maintaining the biosphere, their crashing populations in the wild, farmlands and backyard gardens is alarming. E.O. Wilson famously concluded that, if humans were to go extinct, the biological world would “regenerate back to the rich state of equilibrium that existed 10,000 years ago.” A glimpse of that richness was afforded us during “anthropause” when pandemic lockdowns temporarily caused pollution reductions and resurgences in wildlife. But “if insects were to vanish,” Wilson added. “The environment would collapse into chaos.” More and more around the globe, cases for insect Armageddon are being made. In New Hampshire, researchers in protected forests found beetle populations since the 1970s have plummeted by 80 percent, their species diversity dropping by 40. A Dutch study of butterflies in the Netherlands found comparable decreases in numbers since the end of the 19th century. According to the International Union for Conservation of Nature, nearly half of 2,200 insect species tracked are reportedly in decline, crickets and grasshoppers (order Orthoptera), and odonates (dragonflies and damselflies) among the hardest hit.

U.S. cultural diversity may be a source of pride to many of us, but insects remain the most varied organisms on Earth. Entomologists estimate the million or so insect species classified to date only represent a quarter of those yet to be identified. Ichneumonidae, for instance, a taxonomic family of parasitoid wasps which lay eggs on paralyzed spiders and caterpillars contains more species (100,000 or so) than every vertebrate classification combined. Because Charles Darwin, in a philosophical sidebar, used prolific parasitism to refute Genesis and existences of “beneficent” deities, members of Ichneumonidae are commonly called Darwin wasps. While creation myths and possible benevolence of gods remains a matter of faith and fanciful conjecture, the role of insects in making this planet livable is not. Dependence on insects for survival is an absolute certainty. Whether their accelerating disappearance is due to climate change, pollution in general, pesticides or loss of habitat to farms and sprawling cities (probably all of the above) we and many other forms of life on Earth are doomed without them. Insects are critical links in nearly every terrestrial and freshwater aquatic food chain. Many mammals, from bats and aardvarks to primates and bears, as well as birds, reptiles, amphibians and fish, are insectivorous to some degree. Recent declines in bat and avian populations worldwide are almost certainly correlated to vanishing insects.

Beetles and other insects are also vital decomposers, breaking down and releasing nutrients from animal dung, carrion and decaying vegetation. Anyone who’s prepared a skeletal museum specimen, as I did for a Siberian tiger that died of gangrenous Clostridium infections, knows how dermestid beetles are invaluable in cleaning carcasses for scientific study. Without insect decomposers in the wild, plant and animal waste would linger and accumulate, causing pestilence and delaying vital nutrient recycling throughout ecosystems. Preying on wide ranges of crop-damagers, predatory insects also act as biological controls against agricultural pests. Damsel bugs, for example, can eat a million aphids a day in an acre of cultivated land. Nationwide, the predation not only saves farmers billions of dollars a year in better yields, but lessens the use of toxic pesticides in integrated pest management. Lesser and fewer insecticide applications not only mean reduced exposures to poisonous residues on fruits and vegetables for consumers and farmhands, but also limit non-point source pollutions of soils and streams.

Soil engineering of subterranean insect colonies, most notably ants, termites, and bees, also plays vital roles in aerating hard ground, adding nutrients essential for plant growth, and helping landscapes retain water. Insects are also critical for seed dispersal. In one of countless co-evolutionary relationships between insects and plants, seeds are often equipped with elaiosomes, tiny lipid-, protein-, and vitamin-filled enticements to aid dispersal. Ants transport the seeds, eat the elaiosomes and leave their undamaged cargoes to sprout. Moreover, insects are supreme pollinators. Roughly 90% of flowering plants (75% of cultivated strains) rely on pollination by animals, mostly insects, to propagate.  Without insect pollination, 30-40% food production for humans would be lost. Combined with crop failures from climate extremes incidental to global warming (e.g. higher frequencies of floods and droughts), insect populations in decline are yet another invitation to disaster.

Scott Deshefy is a biologist, ecologist and two-time Green Party congressional candidate.