A worldwide compilation of long-term insect abundance studies shows that the number of land-dwelling insects is in decline. On average, there is a global decrease of 0.92% per year, which translates to approximately 24% over 30 years. At the same time, the number of insects living in freshwater, such as midges and mayflies, has increased on average by 1.08% each year. This is possibly due to effective water protection policies. Despite these overall averages, local trends are highly variable, and areas that have been less impacted by humans appear to have weaker trends. These are the results from the largest study of insect change to date, including 1676 sites across the world, now published in the journal Science.
The study was led by researchers from the German Centre for Integrative Biodiversity Research (iDiv), Leipzig University (UL) and Martin Luther University Halle-Wittenberg (MLU). It fills key knowledge gaps in the context of the much-discussed issue of “insect declines.”
Over the past few years, a number of studies have been published that show dramatic declines in insect numbers through time. The most prominent, from nature reserves in Western Germany, suggested remarkable declines of flying insect biomass (>75% decrease over 27 years). This was published in 2017 and sparked a media storm suggesting a widespread “insect apocalypse.” Since then, there have been several follow-up publications from different places across the world, most showing strong declines, others less so, and some even showing increases. But so far, no one has combined the available data on insect abundance trends across the globe to investigate just how widespread and severe insect declines are. Until now.