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The "windshield 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 received coverage from

Science, BBC News, The Atlantic, The Sydney Morning Herald, The Daily Telegraph, The Guardian, The Washington Post and The New York Times

There appears to be an overall decline in insect populations which seems to be causally related to the anecdotal observations of the lowering of bug related 'windshield casualties'.

To what extent is this due to the decline in insect population versus some other phenomenon e.g. relocation of insects (rather than decline in total populations), aerodynamics of modern cars, etc?

  • 3
    I will offer the anecdotal observation that I've wondered about this. Of course, I don't drive great distances as much as I used to, 50 years ago, and newer cars are more "airstreamed". Not to mention windshield washers. So there are plenty of confounding factors. – Daniel R Hicks Feb 3 at 13:39
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    I went to edit the title - the "non-anecdotal" part of the request is redundant here, and "windshield phenomenon" isn't clear. But what is the claim? I see two. (1) That there is an anecdotal observation that populations have declined with no strong direct physical evidence behind it... but many entomologists have investigated this and claim (2) that insect populations have declined - but you've explicitly rejected that as NOT the subject. Why dismiss precisely the evidence that would support the observations? – Oddthinking Feb 3 at 22:29
  • @Oddthinking i hope the edit is clearer. thanks – bondonk Feb 5 at 8:03
  • What evidence would you accept as answering your question? Do you want a study were they tried to drive an old vs new car through places full of insects and check whether the car shape affects how many end up in the windshields? I don't think any study like this has been done so... – Giacomo Alzetta Feb 5 at 13:32
  • @GiacomoAlzetta I'm not sure where you're going with the comment. If the study has not been done, the question can remain open until such a study is performed. – pipe Feb 5 at 13:37
3

The Question consists of three parts

1: Decline of insect populations. Is there any substantial and robust decline of insects in a large enough space and timespan to consider it a general decline?

The overall abundance of butterfly species in Great Britain has declined by approx 70% in 20 years. http://science.sciencemag.org/content/303/5665/1879/tab-figures-data Other insect groups have declined as well in biodiversity, however not that much as butterflies. http://science.sciencemag.org/content/345/6195/401.full This just means there is a decline of species richness in some key groups, which while alarming, does not mean population decline in general. This study found over a 30- year period a 75% decline of insect biomass in various sampling locations in Germany, however. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0185809#sec001 I could not find follow up studies or similar ones, yet this study seems solidly done and over a large area and timespan account to for variability. So yes, there seem to be a general decline in insect populations.

2. Are there fewer insects smashed on car windshields? Is there substantial evidence for a sufficiently large enough area and timespan?

There is no evidence to compare insect numbers on windshields. BBC did an experiment covered in Wikipedia, which is a good summary of the "Windshield Phenomenon". https://en.wikipedia.org/wiki/Windshield_phenomenon. This experiment is however only of anecdotal value. Humans are highly biased, maybe we remember just those days when our windshield was heavily covered in stains? So far, inconclusive.

3. Does the population decline cause fewer smashed insects?

As we have seen in 2, it is inconclusive if there are really fewer smashed insects. However to prove this causality could be difficult anyways. We would need the numbers of smashed insects of areas that do not have populations decline at least for a correlation. There are a lot of factors to control for, too. But maybe we could show a correlation if the difference is pronounced enough.

Overall, the answer to the question is a NO in the sense that it is not valuable to give an answer as there is no evidence for one of the presumptions.

  • Personal anecdote related to reduction in insect population... I don't think I've ever killed (specifically) a butterfly on my windscreen. – bondonk Feb 5 at 20:39
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There has been a massive decline in the number of insect in the UK over the last 50 years. This is due mainly to the increased use of pesticides in the farming industry and the disappearance of natural habitat for most insects. I have no scientific data only the opinions of my wife who is a professional environmentalist.

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    This would be useful if you did have scientific data. Unfortunately without that, you'll only get downvotes, I reckon. – Rory Alsop Feb 5 at 18:40
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    Some of us want more than "some dude on the internet's wife says ___"... ;) – dandavis Feb 5 at 19:06

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