An international group of scientists have, for the first time, combined data to give a picture of insect abundance around the world.
13 May 2020
A global compilation of long-term insect abundance studies reveals that the number of land-dwelling insects is in decline, at the same time the number of insects living in fresh water, such as midges and mayflies has increased. The study was led by Leipzig University and Martin Luther University, Germany. The body of work, say the researchers, fills key knowledge gaps in the context of the much discussed issue of insect decline.
A number of studies have indicated a fall in the abundance of insects. However, the research team highlighted a study, published in 2017, which concluded that insect populations at nature reserves in West Germany were in decline. The so called ‘insect apocalypse’ sparked a media storm. Since then a number of follow-up studies from around the world, came out with a mixture of findings, most showing strong declines, other less so, and some even showing increases.
Until recently the available data on insect abundance had not been combined to show trends across the globe and investigate how widespread or severe insect decline might be. But now an international team of scientists have collaborated to compile data from 166 long-term surveys carried out at 1676 sites across the world between 1925 and 2018.
The analysis revealed high variation in trends even among nearby sites. So, for example, in countries where many insect surveys have taken place, such as the UK, US and Germany, some sites saw declines in insect abundance while other nearby sites recorded no change or even an increase. However, when all of the trends from around the world were combined, researchers were able to estimate how total insect abundances were changing with time. They found that with terrestrial insects there was an average decrease of 0.92% per year. Insect declines were strongest in the US and Europe, particularly Germany.
At the same time insects that live part of their life in water, showed an average annual increase of 1.08%, corresponding to a 38% increase over 30 years. This positive trend was particularly strong in Northern Europe, western US and Russia.
While the scientists are unable to say for certain why these positive, and negative, trends have emerged, they believe that issues such as habitat destruction and land-use change would have an impact.