Other bugs are disappearing at a rate of just under 1 per cent a year, with lots of variation from place to place, according to the study published in the journal Science.
That’s a tinier population decline than found by some smaller localised studies, which had triggered fears of a so-called insect apocalypse. But it still adds up to something “awfully alarming”, said entomologist Roel van Klink of the German Centre for Integrative Biology, the study’s lead author.
“The decline across insect orders on land is jaw dropping,” said Michigan State University butterfly expert Nick Haddad, who wasn’t part of the study. “Ongoing decline on land at this rate will be catastrophic for ecological systems and for humans. Insects are pollinators, natural enemies of pests, decomposers and besides that, are critical to functioning of all Earth’s ecosystems.”
The number of insects on average has declined in the air, in the grass and on the soil surface, but not in trees or underground, the researchers found.
Projecting the trends into the future shows that land-dwelling insects would sustain a population drop of 24 per cent over 30 years while the freshwater bugs would experience a 38 per cent increase over the same period.
“Insects are a central part of almost all ecosystems because they stand in the middle between the plants they eat and the animals that eat insects, like birds, bats and lizards,” van Klink said.
“They also impact our own lives, often in ways we don’t think about. Insects pollinate many of our crops, and without them we would have no fruits and no flowers. But at the same time, insects transmit terrible diseases like malaria, Zika and West Nile virus, they eat our crops and damage tree plantations,” van Klink added.
The study did not break down the findings by species. There was scant data from South Asia and the Middle East, and limited data from Africa. The strongest declines were documented in the mid-western United States and in Germany.
The researchers credited clean-water policies instituted in recent decades for the increase in freshwater bugs.
They attributed the declines in land-dwelling insects to human activities such as habitat destruction and fragmentation, urbanisation, light pollution and chemical pollution, while saying insecticides and increased droughts due to climate change may also have played a role.