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Scientific studies on the number of insects sprayed on cars have revealed a large decrease. It has plummeted by as much as 80% in two decades
The research adds to mounting evidence for what some scientists have called an "insect apocalypse," which threatens a collapse in the natural world that supports humans and all life on Earth. A third study shows the plummeting of aquatic insects in streams.
The survey of insects hitting car windshields in rural Denmark used data collected each summer from 1997 to 2017 and found an 80% decrease in abundance. He also found a parallel decrease in the number of swallows and martins, birds that live on insects.
The second survey, in the county of Kent in the UK in 2019, examined symbols on a grid affixed to car license plates, known as a 'splatometer'. This revealed 50% fewer impacts than in 2004. The research included vintage cars up to 70 years old to see if their less aerodynamic shape meant they killed more bugs, but found that modern cars actually hit a little more bugs.
"This difference we found is extremely important as it reflects the patterns of decline that are widely reported elsewhere, and insects are absolutely critical to food webs and the existence of life on Earth," said Paul Tinsley-Marshall of the Kent Wildlife Trust. "It's pretty horrible," he added.
"Most naturalists who live in the wild have seen it coming for a long time," said Anders Pape Møller of the University Paris-Suden France, who has visited the Danish study area for 50 years. “My colleagues remember going on summer vacation when the children and their parents had to stop their car to clean the windshield in order to continue. This is certainly no longer a problem. "
Insect population collapses have been reported in Germany and Puerto Rico, and the first global scientific review, published in February 2019, said that widespread declines threatened to cause a "catastrophic collapse of nature's ecosystems." Insects pollinate three-quarters of crops and another recent study showed widespread losses of such insects in Britain.
The causes of the decline are the destruction of natural habitat, pesticides and the impacts of the climate crisis. Light pollution has also been cited as a key “bringer of the insect apocalypse”.
The Kent survey looked at nearly 700 volunteer-reported car trips from June to August 2019. Insect splatters on the registration plate were counted to calculate the number of impacts per kilometer. This was 50% lower than an RSPB survey using the same methodology found in 2004.
"The most surprising thing was how rarely we found anything on the plate," Tinsley-Marshall said. This was despite data showing that modern cars hit more bugs, perhaps because older models push a larger layer of air and insects onto the vehicle.
The Danish research, published in the journal Ecology and Evolution, used data from an average of 65 car trips per year on the same stretch of road and at the same speed between 1997 and 2017. Møller took into account the time of day, temperature , Wind speed and travel date and found an 80% decrease in insect abundance over the 21-year period. Controls with insect nets and sticky traps showed the same trend.
Møller said the causes could be "a little bit of everything," but pointed to significant changes due to global warming. “In my 50 years, the temperature in April, May and June has risen on average 1.5C ° in my study area,” he said. “The amount of rain has increased by 50%. We are talking about dramatic differences. "
The stream's investigation, published in the journal Conservation Biology, analyzed weekly data from 1969 to 2010 on a stream in a German nature reserve, where the only major human impact is climate change.
“In general, the water temperature increased by 1.88C and the discharge patterns changed significantly. These changes were accompanied by an 81.6% decrease in the abundance of insects, ”the scientists reported. "Our results indicate that climate change has already severely altered wildlife communities, including in protected areas."
Matt Shardlow, CEO of the Buglife charity, said: “These new studies reinforce our understanding of the dangerously rapid disappearance of insect life both in air and in water. It is becoming increasingly clear that the four horsemen of the insect apocalypse are climate change, habitat destruction, habitat fragmentation and pollution. It is essential that we create a more united space for insects that is safe from pesticides, climate change and other harm.
Most of the scientific investigations carried out to date have shown serious decreases in the number of insects in the places studied. "There is no question about this," Møller said. "What there is slight doubt about is the extent to which this occurs across geographic and temporal scales."
Long-term studies are rare and mostly from Europe and North America, with some ranging from Australia to China and Brazil to South Africa, but almost nowhere else. The best methodologies have also been debated among researchers.
"But that's not the main point," Tinsley-Marshall said. "I think it's pretty clear that something quite catastrophic is happening." Kent Wildlife Trust is now working on a smartphone app to make it easier for volunteers to provide bug splash data.