The windshield phenomenon (or windscreen phenomenon) is a term given to the anecdotal observation that people tend to find fewer insects smashed on the windscreens of their cars now compared to a decade or several decades ago. This effect has been ascribed to major global declines in insect abundance.
[History] 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 myriad insects.
In 2004 the Royal Society for the Protection of Birds asked British motorists to attach a PVC film to their number plate to measure the number of insects that collided with it during car journeys. This splat-o-meter estimated one insect squashed every five miles of driving, and represents one of the few pieces of data directly relevant to the windscreen phenomenon. Although the study did not have historical data for comparison, it was reported that many participants in the study were astounded by how few insects their traps collected. John Rawlins, head of Invertebrate Zoology at the Carnegie Museum of Natural History has suggested that changes in vehicle design that have made cars more aerodynamic may be partially responsible for any changes in the number of insects hitting windshields. Scott Black, executive director of the Xerces Society for Invertebrate Conservation in Portland, Oregon, does not agree. Speaking in an article published in Science, he says that that the sleek 1969 Ford Mustang that he drove as a teenager was always covered with insects. In 2016 the Canadian naturalist John Acorn noted what 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".
[Studies] The windshield phenomenon was widely discussed in 2017 after major publications and media coverage concerning reductions in insect abundance over the last few decades. Entomologists state that they had noticed that they no longer had to frequently clean their windshields. While data existed demonstrating the long-term decline in numbers of certain species, such as bees and butterflies, data was lacking for overall insect abundance. The Entomological Society of Krefeld, Germany had amassed 27 years worth of flying insect numbers collected using unchanged methods (Malaise traps) and sampling spots, publishing a landmark study in 2017 describing a >75% decrease in total biomass over the years.Another paper a year later showed that this effect was matched in the El Yunque National Forest of Puerto Rico, using abundance data from 1976 and comparing it to that collected in the modern day using identical methods.
Not all the data collected supports such a steep decline of insect abundance, suggesting that the true effect worldwide on insect populations is variable. However, many studies agree with the conclusions of the German investigation suggesting that insect numbers are declining.