In recent years, several studies have been published showing a dramatic decrease in insect numbers over time. The most prominent, of the nature reserves in West Germany published in 2017, suggested a notable decrease in the biomass of flying insects (> 75% decrease in 27 years). Since then, there have been several follow-up investigations from different places around the world, most showing sharp declines, some less, and some even showing increases.
In 2020, an international team of scientists collaborated to collect data from 166 long-term surveys conducted at 1,676 sites around the world, between 1925 and 2018, to investigate trends in insect abundance (number of individuals, not species). The analysis revealed a large variation in trends, even between nearby sites. For example, in countries where a lot of insect studies have been conducted, such as Germany, the United Kingdom, or the United States, some places experienced declines, while others very close showed no change, or even increased. However, when all the trends around the world were combined, the researchers were able to estimate how the total abundance of insects was changing on average over time. They found that for terrestrial insects (insects that spend their entire lives on land, such as butterflies, grasshoppers, and ants), there was an average decrease of 0.92% per year.
The insects are silently disappearing
“0.92% may not seem like a lot, but it actually means 24% fewer insects in 30 years and 50% fewer in 75 years and we don’t realize it from one year to the next,” explains researcher Roel van Klink from the University of Leipzig.
For this work, the experts also analyzed data from many of these hidden habitats. This showed that, on average, there are fewer insects living in grass and soil today than in the past, similar to flying insects. On the contrary, the number of insects that live in the treetops, on average, has remained practically unchanged.
Although scientists have not been able to say with certainty why these negative and positive trends are happening, they were able to point to some possibilities. Most importantly, they found that the destruction of natural habitats, particularly through urbanization, is associated with a decline in terrestrial insects. Other reports, such as the IPBES Global Assessment, also noted that land use change and habitat destruction are a leading cause of global change in biodiversity.
It is clear that greater urgency is required in the protection against insects of which today we will know those that cause us the most fear, the most lethal and poisonous on the planet.
