Anyone who has watched moths and other flying insects bashing themselves against street lights may have noticed something in recent years: The clouds around the sodium lamps just don’t seem as big as they used to.
It has also happened with windshields: After long drives, the glass is far less insect-smeared than it used to be. Scientists have noticed too. And as Ed Yong writes for The Atlantic, a new study quantifies this decline in some of Germany's nature reserves, showing that local populations of flying insects have decreased by about 76 percent in the last 27 years.
Since 1989, researchers from the Entomological Society Krefeld have annually collected insects in protected natural areas around West Germany, Yong reports. The group uses malaise traps, which consist of large fabric tents that funnel insects into a bottle of alcohol for preservation. But over the years, the Society noticed they were collecting fewer and fewer specimens. So they took a look at their data, which includes 1,503 traps located in 63 locations—swamps, grasslands, dunes and many other habitat types.
The researchers found that the weight of the insects collected between May and October fell by a seasonal average of 76 percent over the course of almost three decades. Summer had an even larger decline. During these months, when flying insect activity should be highest, the total weight of insects dropped by 82 percent. They published their results in the journal PLOS One.
“This decline happened in nature reserves, which are meant to preserve biodiversity and ecosystem functioning,” first author of the paper Caspar Hallmann of Radboud University in the Netherlands tells Ben Guarino at The Washington Post. “This is very alarming!”
It’s hard to pinpoint the exact reason for the decline. As Yong reports, the researchers were not able to correlate the declines with habitat loss or climate change. It was also difficult to link the decline to weather patterns. According to Guarino, it’s possible that changes in fertilizer and pesticide use in surrounding agricultural lands could have an impact. It’s also possible the insects migrated to other areas.
"There is an urgent need to uncover the causes of this decline, its geographical extent, and to understand the ramifications of the decline for ecosystems and ecosystem services," the researchers write in the study.
Other studies has shown similar dramatic declines in certain insect populations in other parts of the world. European grassland butterflies have dropped by 50 percent in the last two decades. A recent study shows that monarchs in the United States have dropped by 90 percent in the east and 97 percent in the west. According to a 2014 study, the abundance of invertebrates around the world has dropped 45 percent in the last 40 years.
The decline is concerning for many reasons. As Euan McKirdy at CNN reports, 60 percent of bird species depend on insects and 80 percent of plants need insects for pollination. “If you like to eat nutritious fruits and vegetables, you should thank an insect. If you like salmon, you can thank a tiny fly that the salmon eat when they're young,” Scott Black, executive director of the insect protection group Xerces Society, tells Guarino. “The whole fabric of our planet is built on plants and insects and the relationship between the two.”
Whatever the cause, Tanya Latty, a research fellow in entomology at Sydney University, tells McKirdy of CNN that policy makers and farmers need to start addressing the insect declines. “The first step is acknowledging that we have a problem, and working to correct that — how do we design our agriculture to encourage insects?” she says. “It could be something as simple as growing wildflowers along the edges of fields.”