The world is a teeming, buzzing, biting web of life, everything dependent on everything else in some often unrecognizable way, and a new study documenting a vast decline in flying insects across Germany has scientists fretting over the broader implications.
Over more than a quarter century of observation across 63 German nature reserves, a team of ecologists based at Radboud University found a whopping 76% decline in the total mass of flying insects. The decline was even more precipitous—82%—in the middle of the summer when insect numbers peak. The authors are alerted both by how this exceeds the 58% estimated decline in the global abundance of wild vertebrates over a similar time period, and how it shows that not only are attention-grabbing insects—butterflies, bees, and moths—in decline, but that there’s a parallel “severe loss of total aerial insect biomass,” suggesting the overall flying insect community “has been decimated over the last few decades.”
Dr. Caspar Hallmann, with Radboud University in the Netherlands, told Earther they were “highly surprised” by the severe declines particularly because they happened in protected areas “that are meant to preserve biodiversity and ecosystem functioning.”
Equally worrisome is the lack of a specific cause, though the authors suggest that the destruction of wild areas and pervasive pesticide use are probably the primary drivers—and that climate change may play a significant role. Many of the natural areas that the researchers monitored are surrounded closely by agricultural enterprises where pesticides are in regular use. This could be causing an “ecological trap,” according to the authors, who consider the results of their analysis to most likely be representative of much of Europe and other areas of the globe where nature reserves butt up against agricultural landscapes.
“Lack of insects is very likely to be detrimental to the entire ecosystem, in terms of its diversity as well as its stability and functioning,” said Hallman. “Insects play a crucial role in ecosystems, being responsible for plant pollination and nutrient recycling as well as acting as a food source for animals such as birds, amphibians, reptiles, bats and small mammals.”
The research, published in the journal Plos One, employs the work of dozens of amateur entomologists that have helped collect data over the past 27 years, by capturing flying insects in special tents called Malaise traps and weighing their total biomass.
According to the study, while current data suggest an overall pattern of decline in insect diversity and abundance, most of this research is confined to very limited areas or specific, well-studied taxa, such as bees. The study gives the example of European grassland butterflies having declined in abundance by an estimated 50% between 1990 and 2011.
The authors assert that “declines of individual species or taxa may not reflect the general state of local entomofauna:”
The total insect biomass would then be a better metric for the status of insects as a group and its contribution to ecosystem functioning...Hence, to what extent total insect biomass has declined, and the relative contribution of each proposed factor to the decline, remain unresolved yet highly relevant questions for ecosystem ecology and conservation.
Hallmann and the other researchers hope their findings will offer some sort of wake-up call, help reduce pesticide use, and increase awareness of the importance of having natural flora, such as wildflowers, surrounding nature reserves, rather than just cropland.
Ulrich Mueller, a professor of integrative biology at the University of Texas who was not involved in the study, told Earther he was surprised by the magnitude of the decline, but not the decline itself.
“The decline is expected given the widespread use of pesticide in agriculture, the increase in general pollutants, and the increase in nighttime lighting that attracts and disrupts night-flying insects,” he said.