When was the last time you saw a glow-worm? Probably quite some time ago. The light-emitting insects have been declining across the world for decades. But they aren’t the only insects to be struggling, according to a new study.
Researchers carried out the largest evaluation of insect abundance across the globe to date, showing that there has been a drop of 25% in their numbers over the last 30 years. Accelerating declines in Europe are what surprised scientist the most.
Using data from 166 long-term surveys across 1,676 sites, the study painted a picture of the state of insect health. While some species were the exception and expanded, such as freshwater insects, they represent a small number among all species.
Researchers also warned that there are insects that remain critically understudied in many parts of the world, such as South America, Asia, and Africa. There’s a lack of data from those regions and activities such as farming and deforestation could be reducing the number of insects there further.
The decline in the number of insects could already be having a large impact on the world as a whole, the new study warned. Insects are the most varied and abundant animals and are very important for all ecosystems, as they pollinate plants and act as food for other animals.
The previous largest assessment, based on 73 studies, led scientists to warn of "catastrophic consequences for the survival of mankind” if insect losses were not halted. The rate of decline seen in the new study was more than double that previously estimated. Other experts estimate 50% of insects have been lost in the last 50 years.Roel van Klink, of the German Centre for Integrative Biodiversity Research in Leipzig, who led the research, told The Guardian:
"This 24% is definitely something to be concerned about. It’s a quarter less than when I was a kid. One thing people should always remember is that we really depend on insects for our food."
The losses were strongest in the US West, Midwest, and in Europe, especially in Germany. Trends in Europe have become more negative in recent years, with the biggest declines since 2005. Elsewhere, data is much sparser, but the expansion of cities is likely having a big negative effect.
Losses of insects are mainly driven by habitat destruction, the use of pesticides, and light pollution, the study showed. The impact of the climate crisis was not clear in the research. Van Klink said changes in heat and rain could harm some species while boosting others, even in the same location.
The finding of habitat destruction has been echoed in other major pieces of research on biodiversity, including last year's IPBES Global Assessment -- which argued that one million animal and plant species are now threatened with extinction due to human action.
Matt Shardlow, the head of the conservation charity Buglife, told The Guardian: “Many insect species are threatened with extinction and this study shows insect abundance is also declining at an unsustainable rate. While the estimate in this study is lower than some, it is still very steep.”
The study was published in the journal Science.