Insect populations suffer “death by a thousand cuts,” and many fall into “terrifying” rates that “tear the carpet of life,” scientists behind a new series of studies said.
The insects face multiple, overlapping threats, including the destruction of wild habitats for agriculture, urbanization, pesticides and light pollution. Population collapse has been recorded in places where human activities are predominant, such as Germany, but there is little data from outside of Europe and North America and especially from wild, tropical regions where most insects live.
The scientists are especially concerned that the climate crisis is causing serious damage in the tropics. But while much more data is needed, the researchers say enough is already known to take urgent action.
Insects are by far the most varied and abundant animals on the planet, with millions of species and 17 times heavier than humans. They are essential to the ecosystems on which humanity depends, as they pollinate plants, provide food to other creatures and recycle nature’s waste.
The studies show the situation is complex: some insect populations are on the rise, such as those whose range is expanding as global warming curbs cold winter temperatures and others are recovering from low levels as pollution in water bodies is reduced.
The good news is that the increased profile of insects declining over the past two years has prompted government action in some places, the scientists said, while a “ phenomenal ” number of citizen scientists are helping with the daunting challenge of studying these tiny creatures.
The 12 new studies are published in the journal Proceedings of the National Academy of Sciences. “Nature is under siege [and] most biologists agree that the world has reached its sixth mass extinction event, ”concludes the main analysis in the package. Insects suffer from ‘death from a thousand cuts’ [and] severe decline in insects can potentially have global ecological and economic consequences. “
Prof David Wagner of the University of Connecticut in the US, the lead author of the analysis, said the abundance of many insect populations was declining by 1-2% per year, a percentage that should not be considered small: 10-20% of your losing animals in a decade and that’s just absolutely scary. You’re tearing apart the carpet of life. “
Wagner said most of the causes of insect decline were known. “But there is one very big unknown and that is climate change – that is the one that scares me the most.” He said greater variability in climate could be ‘driving’ [insect] extinction at a rate that we have not seen before ”.
“Insects are very sensitive to drought because they are all superficial and have no volume,” Wagner said. “Things like dragonflies and damselflies can dry to death within an hour with very low humidity.”
One study identifies an increasingly erratic climate as the overarching reason for the loss of moths and other insects in the forests of northwestern Costa Rica since 1978. This could be a “harbinger of the wider fate of Earth’s tropical forests.” Wagner said.
However, another study contradicts a 2018 report of a 98% insect collapse in a Puerto Rican forest. The new paper says “abundance is generally not declining,” and that changes in populations are driven by the effects of hurricanes, not climate change. Brad Lister, who led the 2018 study, said he was not convinced of the work, but would conduct his own analysis of the data used and submit the conclusion to the PNAS editors.
Wagner said the increased public attention had led to action such as an EU initiative to protect pollinators, a $ 118 million commitment to insect conservation in Germany and $ 25 million in Sweden.
Another document describes actions that can protect insects. Individuals can redesign their gardens, reduce pesticide use and limit outdoor lighting, he said, while countries need to reduce the impact of agriculture. All groups can help change attitudes toward insects by conveying that they are critical components of the living world.
The largest systematic review of global insect dosage to date, published in April 2020, showed a fall of nearly 25% over the past 30 years, with an accelerating decline in Europe. It indicated that terrestrial insects were declining by nearly 1% per year. The previous largest review, based on 73 studies, prompted the researchers to warn of “catastrophic consequences for humanity’s survival” if insect losses were not halted. It estimated the decline at 2.5% per year.
Other PNAS papers found both declines and increases. The number of butterflies has fallen by 50% in the UK since 1976 and by 50% in the Netherlands since 1990, one said. It also showed that the number of butterflies began to decline a long time ago, with an 80% decline between 1890 and 1940. However, a study of moths showed zero or only a modest long-term decline over the past two decades in Ecuador and Arizona, USA.
“The most important thing we learn [from these new studies] the complexity behind insects is decreasing. No quick solution will solve this problem, ”says Roel van Klink of the German Center for Integrative Biodiversity Research.. “There are certainly places where the number of insects is decreasing sharply, but not everywhere. This is cause for hope, as it can help us understand what we can do to help them. They can bounce back very quickly if conditions improve. “
Wagner said, “We know nature is under attack and we know we are responsible – we don’t really need much more data to change what we do. It is unscrupulous what can happen if we don’t pay attention and change the way we consume. “
Another article in the series, co-authored by Wagner, concluded, “ To mitigate the effects of the sixth mass extinction we caused, we need: a stable (and almost certainly lower) human population, sustainable levels of consumption and social justice empowering the less wealthy people and nations of the world, where the vast majority of us live. ”