January 23, 2019

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The Insect Apocalypse Is Here

The Insect Apocalypse Is Here
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Bugs are vital to the decomposition that keeps nutrients cycling, soil healthy, plants growing and ecosystems running. This role is mostly invisible, until suddenly it’s not. After introducing cattle to Australia at the turn of the 19th century, settlers soon found themselves overwhelmed by the problem of their feces: For some reason, cow pies there were taking months or even years to decompose. Cows refused to eat near the stink, requiring more and more land for grazing, and so many flies bred in the piles that the country became famous for the funny hats that stockmen wore to keep them at bay. It wasn’t until 1951 that a visiting entomologist realized what was wrong: The local insects, evolved to eat the more fibrous waste of marsupials, couldn’t handle cow excrement. For the next 25 years, the importation, quarantine and release of dozens of species of dung beetles became a national priority. And that was just one unfilled niche. (In the United States, dung beetles save ranchers an estimated $380 million a year.) We simply don’t know everything that insects do. Only about 2 percent of invertebrate species have been studied enough for us to estimate whether they are in danger of extinction, never mind what dangers that extinction might pose.

When asked to imagine what would happen if insects were to disappear completely, scientists find words like chaos, collapse, Armageddon. Wagner, the University of Connecticut entomologist, describes a flowerless world with silent forests, a world of dung and old leaves and rotting carcasses accumulating in cities and roadsides, a world of “collapse or decay and erosion and loss that would spread through ecosystems” — spiraling from predators to plants. E.O. Wilson has written of an insect-free world, a place where most plants and land animals become extinct; where fungi explodes, for a while, thriving on death and rot; and where “the human species survives, able to fall back on wind-pollinated grains and marine fishing” despite mass starvation and resource wars. “Clinging to survival in a devastated world, and trapped in an ecological dark age,” he adds, “the survivors would offer prayers for the return of weeds and bugs.”

But the crux of the windshield phenomenon, the reason that the creeping suspicion of change is so creepy, is that insects wouldn’t have to disappear altogether for us to find ourselves missing them for reasons far beyond nostalgia. In October, an entomologist sent me an email with the subject line, “Holy [expletive]!” and an attachment: a study just out from Proceedings of the National Academy of Sciences that he labeled, “Krefeld comes to Puerto Rico.” The study included data from the 1970s and from the early 2010s, when a tropical ecologist named Brad Lister returned to the rain forest where he had studied lizards — and, crucially, their prey — 40 years earlier. Lister set out sticky traps and swept nets across foliage in the same places he had in the 1970s, but this time he and his co-author, Andres Garcia, caught much, much less: 10 to 60 times less arthropod biomass than before. (It’s easy to read that number as 60 percent less, but it’s sixtyfold less: Where once he caught 473 milligrams of bugs, Lister was now catching just eight milligrams.) “It was, you know, devastating,” Lister told me. But even scarier were the ways the losses were already moving through the ecosystem, with serious declines in the numbers of lizards, birds and frogs. The paper reported “a bottom-up trophic cascade and consequent collapse of the forest food web.” Lister’s inbox quickly filled with messages from other scientists, especially people who study soil invertebrates, telling him they were seeing similarly frightening declines. Even after his dire findings, Lister found the losses shocking: “I didn’t even know about the earthworm crisis!”

The strange thing, Lister said, is that, as staggering as they are, all the declines he documented would still be basically invisible to the average person walking through the Luquillo rain forest. On his last visit, the forest still felt “timeless” and “phantasmagorical,” with “cascading waterfalls and carpets of flowers.” You would have to be an expert to notice what was missing. But he expects the losses to push the forest toward a tipping point, after which “there is a sudden and dramatic loss of the rain-forest system,” and the changes will become obvious to anyone. The place he loves will become unrecognizable.

The insects in the forest that Lister studied haven’t been contending with pesticides or habitat loss, the two problems to which the Krefeld paper pointed. Instead, Lister chalks up their decline to climate change, which has already increased temperatures in Luquillo by two degrees Celsius since Lister first sampled there. Previous research suggested that tropical bugs will be unusually sensitive to temperature changes; in November, scientists who subjected laboratory beetles to a heat wave reported that the increased temperatures made them significantly less fertile. Other scientists wonder if it might be climate-induced drought or possibly invasive rats or simply “death by a thousand cuts” — a confluence of many kinds of changes to the places where insects once thrived.

Like other species, insects are responding to what Chris Thomas, an insect ecologist at the University of York, has called “the transformation of the world”: not just a changing climate but also the widespread conversion, via urbanization, agricultural intensification and so on, of natural spaces into human ones, with fewer and fewer resources “left over” for nonhuman creatures to live on. What resources remain are often contaminated. Hans de Kroon characterizes the life of many modern insects as trying to survive from one dwindling oasis to the next but with “a desert in between, and at worst it’s a poisonous desert.” Of particular concern are neonicotinoids, neurotoxins that were thought to affect only treated crops but turned out to accumulate in the landscape and to be consumed by all kinds of nontargeted bugs. People talk about the “loss” of bees to colony collapse disorder, and that appears to be the right word: Affected hives aren’t full of dead bees, but simply mysteriously empty. A leading theory is that exposure to neurotoxins leaves bees unable to find their way home. Even hives exposed to low levels of neonicotinoids have been shown to collect less pollen and produce fewer eggs and far fewer queens. Some recent studies found bees doing better in cities than in the supposed countryside.

The diversity of insects means that some will manage to make do in new environments, some will thrive (abundance cuts both ways: agricultural monocultures, places where only one kind of plant grows, allow some pests to reach population levels they would never achieve in nature) and some, searching for food and shelter in a world nothing like the one they were meant for, will fail. While we need much more data to better understand the reasons or mechanisms behind the ups and downs, Thomas says, “the average across all species is still a decline.”



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