Windshield Phenomenon

Decline in insect populations

The windshield phenomenon is a recent observation that fewer dead insects accumulate on the windshields of people’s cars. It has been attributed to a global decline in insect populations caused by human activity.

As early as the 2000s, it became a commonplace observation among drivers that windscreens after a long drive no longer had to be cleaned of a myriad of insects. In 2016, Canadian naturalist John Acorn noted that the phenomenon had recently become a meme but questioned whether it is ‘reasonable to assume that windshields can tell us something about the overall numbers of insects’ and also that ‘humans are notoriously bad at detecting trends.’

A 20-year study measured the number of dead insects on car windscreens on two stretches of road in Denmark from 1997 until 2017. Adjusted for variables such a time of day, date, temperature, and wind speed, the research found an 80% decline in insects. A parallel study using sweep nets and sticky plates in the same area positively correlated with the reduction of insects killed by car windscreens.

In 2004 the Royal Society for the Protection of Birds (RSPB) asked 40,000 motorists in the United Kingdom to attach a sticky PVC film to their number plate. One insect collided with the plate for every 5 mi driven. A follow-up study by Kent Wildlife Trust in 2019 used the same methodology as the RSPB survey and resulted in 50% fewer impacts. The research also found that modern cars, with a more aerodynamic body shape, killed more insects than boxier vintage cars.

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