Declines in insect biomass

I had a surreal conversation with my (conservative) uncle this Christmas. It went a little like this:
Me: A study in Germany this year showed a large decline in insect biomass…75% over the past thirty years or so (Hallmann et al 2017, open access). We call it the “windscreen effect“, where when you used to drive through the country, your windshield would be covered in insect splatters, but now that does not happen as much.
Uncle: Riiiiiiiiiiiiiight it’s not just that the shape of the windshield has changed.
Me: What? No, the study showed a large decline in total insect biomass. There are several other studies also showing declines in certain insect groups. It probably has something to do with the enormous global use of pesticides in agriculture.
Uncle: Suuuuuure… *rolls his eyes and walks away*

Thinking back on this befuddling conversation later, I wish I’d been more clear that the scientists did not collect the data from windshields…that’s just the example we use to explain it. At the time, I thought I was clear on that, but now I’m not so sure. It can be difficult to be as clear as you intend when discussing these topics with family (and not just because my uncle was agonizingly patronizing with me).

Regardless, I’m not sure I could have convinced my uncle that these scientific studies were valid (and I doubt he’d read them if I forwarded them to him). It can be difficult to step outside your belief system, and it’s important to recognize that some people will simply never accept that humans are having a dramatic impact on ecosystems around the world, in spite of the wealth of evidence. And, okay, yes, popular press has done some damage to the message by overblowing the significance of the German study (calling it “ecological Armageddon” sigh), but this always happens.

Agricultural lands occupy more than 40% of the terrestrial surface of the Earth. In terms of ecological impact, these lands have huge potential. And they are some of the most intensively managed ecosystems on Earth. We (attempt to) control the inputs, the outputs, the species composition, soil quality, water access, and even pathogens and pests. Never mind the fact that industrial agriculture (i.e. the majority of agricultural land cover) tends to focus on monocultures; these are still incredibly complex, difficult to control systems. Hence, pesticide use.

FAO data shows that we use more than 2.6 million tonnes of pesticides (some awesome graphs here) every year, over more than 40% of the surface of the Earth…is there any wonder there are declines in insect biomass? That is, in fact, the objective of insecticides. So I guess the thing that is difficult to understand, from my perspective, is why anyone would be surprised by studies showing declines in insect biomass.

It is of course important not to confound biomass and diversity. There is the potential for some insect groups to increase in abundance while others decrease in abundance. A decline in biomass does not *necessarily* mean species richness (number of species) has declined, though other studies have suggested as much. But insect biomass is important in itself, as insects are the primary food for much of the rest of the trophic web, including insectivorous birds, bats, mammals, reptiles, and amphibians.

Judge for yourself, here are some selected studies from hundreds I could put here:

  1. Significant declines in some, but not all sites in the UK (Shortall et al 2009, open access)
  2. 75% declines in protected areas in Germany over past 30 years (Hallmann et al 2017, open access)

Several popular press articles on the decline of insectivorous birds:

  1. Why are big, insect-eating birds disappearing? Maybe we’re running low on bugs.
  2. ‘Catastrophe’ as France’s bird population collapses due to pesticides
  3. Europe faces ‘biodiversity oblivion’ after collapse in French birds, experts warn
  4. Bug diet of birds has dramatically declined in quality, researchers find (science article:

Specific groups:

  1. UK moths (Conrad et al 2004)
  2. UK birds, butterflies, moths (Thomas et al 2004)
  3. Global dragonflies and damselflies (Clausnitzer et al 2009)
  4. UK carabid beetles (Brooks et al 2012)
  5. UK aculeate pollinators (Ollerton et al 2014)
  6. Butterflies Barro Colorado Island (Bassett et al 2015, open access)
  7. Bees in general (Goulson and Nicholls 2016)
  8. Bumblebees (Williams and Osbourne 2009)
  9. Britain/Netherlands pollinators/plants (Biesmeijer et al 2009)

7 thoughts on “Declines in insect biomass

  1. There are some people you will never be able to educate – I can think of a few myself!He talks Have you read “The Moth Snowstorm” by Michael McCarthy? He talks of the windshied affect at the start of his book.

  2. Thank you for this information. I did not realize there was a decline, except in bees. A lot of provinces in Canada have banned pesticide use on home gardens and lawns, but farmers are still OK to spray away… It is time for change.

      • Maybe he just didn’t care because he can’t see the big picture – and doesn’t want to. Some people just want to see their tiny world and what is good for them personally and not what is good for us all collectively.

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