German researchers have found the number of land-dwelling insects is on the decline while the number of insects living in freshwater has increased.
The researchers compiled counts from studies around the world between 1925 and 2018. They found that the population of land-dwelling insects has decreased by .92% a year. That means in 30 years, the population of insects living on land will have decreased by 24%.
Lead author Roel van Klink said 0.92% may not sound like much, but it means 24% fewer insects in 30 years’ time and 50% fewer over 75 years.
“Insect declines happen in a quiet way, and we don’t take notice from one year to the next,” he said. “It’s like going back to the place where you grew up. It’s only because you haven’t been there for years that you suddenly realize how much has changed, and all too often not for the better.”
At the same time, the populations of freshwater insects like dragonflies and mosquitoes are increasing by an average of 1.08% a year. The positive trend was the strongest in Northern Europe, the western U.S. and Russia.
“Insect populations are like logs of wood that are pushed under water,” van Klink said. “They want to come up, while we keep pushing them further down. But we can reduce the pressure so they can rise again. The freshwater insects have shown us this is possible.”
The scientists say the destruction of natural habitats through urbanization and land-use change may be the main causes of the global biodiversity change.