Science Matters

(1/2022) News of an insect Armageddon, as some labeled it, burst into popular consciousness in 2017 when researchers in Germany claimed to have found drastic declines in the insect populations in two nature reserves. The news spread like the Delta variant or maybe even Omicron. Soon afterward even as sober a news organization as The New York Times ran a major article headlined: "The Insect Apocalypse is Here."

The metaphors vary, but the message from popular media has been fairly consistent: A mass extinction of insects is underway, and the demise of this essential group of species imperils all other living things on Earth.

Whether the situation is as dire as that, the claims may have heightened your awareness if, for example, you were washing your car’s windshield and realized there are no smeared bug corpses. Or maybe it came to you when you left the porchlight on last summer and noticed that there weren’t many insects swarming around it. Or maybe 2021 was the first year in which your roses bloomed happily without the usual devastation by Japanese beetles. All three of these happened to me. No matter how it came to you, environmental activists say, such observations were your local window onto a global phenomenon.

But science matters, and a look at the totality of the evidence leads to a different conclusion. The bottom line is that while populations of some insect species are declining in some places, including some highly visible species, there is no solid evidence of a wide-ranging decline nor of anything approaching imminent extinction of the whole insect class. Not even by a century from now do professional entomologists (specialists in insects) forecast that all—or even most—insect species will be wiped out. In fact, populations of some species are currently increasing.

The truth, as is so often the case in environmental matters, is complicated. Let’s step back for a moment to 2017. That’s when claims of imminent catastrophe burst into public view.

In that year two environmental activists published a study of two nature reserves in Germany in which they found some species declined more than 75 percent over the course of 30 years. That triggered the avalanche of other reports of various species in scattered parts of the world. But, as critics have pointed out, those findings in Germany were based on the total weight of insects caught in traps set in different parts of the country as measured at different times of year through the decades. Incidentally, the traps caught only flying insects.

Many scientists would have found it more credible if there had been repeated trapping at the same spots. In science, you want your before-and-after comparison to have exactly the same circumstances in both cases with only one variable—in this case, time. Moreover, to make a broad claim, it would have been better to use traps that also caught crawling insects.

Here’s an illustration. If you count the flying bugs that died on your windshield this week and compare it to the number of pests crawling on your roses last year, your finding will be nonsense. Even if you compare windshield bugs this last June to windshield bugs the previous June, you will still have poor methodology. Weather could have been very different, and we know insect populations are sensitive to weather. You get the point.

And yet, for all the methodological cautions, there really are many credible scientific reports of insect declines in various parts of the world and in different habitats. Entomologists and others have been sounding alarms for many years.

The Number One culprit, scientists have found, is habitat loss. Forests are cleared. Wild meadows become residential subdivisions. Streetlights disrupt the feeding and reproductive behavior of many insect species. There is no mystery about why this is happening. Human activity—most of it unavoidable where populations of our species are growing—is to blame. Urbanization, to name it in one word.

The second most cited cause is chemical pollution, especially by pesticides and fertilizers. Again, these materials are used where people live, garden and farm, thus affecting insect species that live close enough for us to notice. If they have any effect in wild areas, we are unlikely to be aware.

Interestingly, most studies in temperate zone ecosystems find no significant effect of climate change. In the tropics the situation is different.

From at least one part of the world far from urbanization comes a worrisome report of insect declines—a World Heritage conservation site in northwestern Costa Rica called Area de Conservacion Guanacaste (ACG). It is a huge area covering a range of habitats from the Pacific coast across dryland forests and up mountain slopes to dripping cloud forests. Two scientists who have worked there for decades published this conclusion in the Proceedings of the National Academy of Sciences last year:

"As human biomonitors, or ‘insectometers,’ we see that ACG’s insect species richness and density have gradually declined since the late 1970s, and more intensely since about 2005. The overarching perturbation is climate change. It has caused increasing ambient temperatures for all ecosystems; more erratic seasonal cues; reduced, erratic, and asynchronous rainfall; heated air masses sliding up the volcanoes and burning off the cloud forest; and dwindling biodiversity in all ACG terrestrial ecosystems."

And yet, as alarming as such reports are, scientists who examine the totality of evidence on a global scale say that the data are not yet as comprehensive or powerful as some environmental activists assert.

"Some of the claims extrapolated from these reports in the media have been extended well past the limits of the data or have been otherwise over-hyped," according to a statement from the Entomological Society of America, the largest organization of scientists studying insects. "The underlying science does not indicate that a global ‘insect apocalypse’ is anywhere near imminent."

Perhaps the most common complaint of entomologists is that we don’t know enough about what is actually happening.

"There is an urgent need for more data, particularly longitudinal studies, research that looks at insect population changes over time," says Robert Peterson, an entomologist at Montana State University and president of the Entomological Society. "Without more study to clarify the geographic scope and magnitude of insect declines, we quite simply don't know what we don't know. It's true that people and all life on earth would be doomed if insects were to disappear. But that is most likely not an immediate danger."

Uncertainty is a common state of affairs in cutting-edge science. We know that human activity is destroying insect habitats in some places, but our local windows on a possibly global phenomenon lie entirely within those damaged habitats. As individuals, we don’t see phenomena on a global scale. We must take the word of researchers who aggregate data gathered consistently from many locations over a long period of time.

While most of the habitat-destroying effects of urbanization are local, global warming and the resulting changes in climate are global. Local or global, as Pogo, the cartoon character said 60 years ago, "We have met the enemy, and he is us."

Rensberger is a retired science journalist from The New York Times and The Washington Post. He welcomes comments or questions at boycerensberger@gmail.com.