While scientists have observed the worldwide decline of insects over the last decades, a new study shows that the big picture is more complicated than they thought. The study, published in Science, drew on data from 166 surveys from 1,676 sites.

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Some of the broad findings were that, while the number of land-dwelling insects is going down, freshwater bugs are increasing. And if you’ve noticed a decrease in bugs splattering your windshield, you’re right. “Our analysis shows that flying insects have indeed decreased on average,” said Jonathan Chase of the German Centre for Integrative Biodiversity Research, one of the study’s authors.

Insects are extremely diverse, with many species filling key roles on the planet, such as recycling nutrients, aerating soil and pollinating plants. The study shows how nuanced and mysterious insects are, with many hiding away under the soil, in tree canopies and on riverbanks. Surprisingly, even when bugs live close together geographically, some populations can be thriving while nearby members of the same species are floundering.

The study found that overall, terrestrial insects such as ants, butterflies and grasshoppers were decreasing by 0.92% per year. This equals 9% per decade. “That is extremely serious, over 30 years it means a quarter less insects,” said the study’s lead author Dr. Roel Van Klink, of the German Centre for Integrative Biodiversity Research. “And because it’s a mean, there are places where it is much worse than that.” Bug decline was particularly severe in Western and Midwestern regions of the U.S., and Europe, especially Germany.

a line of red ants walking across a tree branch

The increase in freshwater insects such as midges and mayflies was one bright note in the study — assuming you’re not sunbathing on a lakeshore. Their populations were growing by about 1.08% per year. Freshwater insects were especially trending in the western U.S., northern Europe and Russia. Researchers credited this population growth to legislation that has cleaned polluted lakes and rivers. “We believe that because we see these increases in fresh water insects, that are related to legislation being put in place, it makes us hopeful that if we put in place the right types of legislation for land insects we can also make them recover,” said Van Klink.

Even the terrestrial insects could still make a comeback, Van Klink said. “The nice thing about insects is that most have incredibly large numbers of offspring, so if you change the habitat in the right way we will see them recover really fast.”

+ BBC

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