One study on a German nature reserve found insect biomass (e.g., kilograms of insects you’d catch in a net) has declined 75% over the last 27 years. Here’s a good summary that answered some questions I had about the study itself.
Another review study found that, globally, invertebrate (mostly insect) abundance has declined 35% over the last 40 years.
Insects are important, as I’ve been told repeatedly (and written about myself). So this news begs a very important and urgent question:
Why aren’t we all dead yet?
This is an honest question, and I want an answer. (Readers will know I take catastrophic possibilities very seriously.) Insects are among the most numerous animals on earth and central to our ecosystems, food chains, etcetera. 35%+ lower populations are the kind of thing where, if you’d asked me to guess the result in advanced, I would have expected marked effects on ecosystems. By 75% declines – if the German study reflects the rest of the world to any degree – I would have predicted literal global catastrophe.
Yet these declines have been going on for apparently decades apparently consistently, and the biosphere, while not exactly doing great, hasn’t literally exploded.
So what’s the deal? Any ideas?
Speculation/answers welcome in the comments. Try to convey how confident you are and what your sources are, if you refer to any.
(If your answer is “the biosphere has exploded already”, can you explain how, and why that hasn’t changed trends in things like global crop production or human population growth? I believe, and think most other readers will agree, that various parts of ecosystems worldwide are obviously being degraded, but not to the degree that I would expect by drastic global declines in insect numbers (especially compared to other well-understood factors like carbon dioxide emissions or deforestation.) If you have reason to think otherwise, let me know.)
Sidenote: I was going to append this with a similar question about the decline in ocean phytoplankton levels I’d heard about – the news that populations of phytoplankton, the little guys that feed the ocean food chain and make most of the oxygen on earth, have decreased 40% since 1950.
But a better dataset, collected over 80 years with consistent methods, suggests that phytoplankton have actually increased over time. There’s speculation that the appearance of decrease in the other study may have been because they switched measurement methods partway through. An apocalypse for another day! Or hopefully, no other day, ever.
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Eukaryote Writes Blog 
(Apologies that I haven’t read most of the sources you cite. Maybe they disagree with some of my comments.)
I’m wary of including links here, lest my comment get eaten by the spam detector 🙂 , but in a piece of mine titled “Humanity’s Net Impact on Wild-Animal Suffering”, subsection “Krefeld Entomological Society insect decline”, I mention that the insect declines seem to apply to flying insects, which doesn’t necessarily imply anything about soil invertebrates. And of course, there’s also uncertainty over how well the Krefeld results generalize even to flying insects elsewhere, though as you mention, there is evidence of declines in other regions.
My guess is that ecologists like to overstate the importance of charismatic animals to ecosystems, including flying insects. Maybe they feed some birds and stuff, but birds also aren’t that important to ecosystems. (Non-human vertebrates are generally tiny footnotes to Earth’s ecology, which is dominated by plants, bacteria, and fungi.)
The paper “A Comparative Analysis of Soil Fauna Populations and Their Role in Decomposition Processes” says: “The soil fauna appears generally to be responsible for less than about 5% of total decomposer respiration” (p. 288). I assume that fungi/bacteria/actinomycetes/etc. account for most of it. In many composting operations, invertebrate animals are minor contributors to decomposition, mainly helping to speed up the process by mechanical breakdown of large pieces of organic matter. So it seems you don’t really need insects for nutrient cycling.
Pollination is a different story, but I guess that’s often done with human-managed bees for certain crops. And trees + grasses are often wind-pollinated.
It’s plausible that human activities like crop cultivation and planting non-native grasses on lawns represent much bigger changes to an ecosystem than reduction in insect populations, since the whole ecosystem is being changed from the base of the food pyramid on up. Nonetheless, “life, uh, finds a way” to make those new ecosystems work.
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Do you mean “why hasn’t the insect die off led to a Homo sapiens die off?” or “why hasn’t the cause of the insect die-off caused us to die off too? Either way, the answer is that it’s still early days.
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Insects have been dying off globally from environmental chemistry change. It also effected bacteria, micro invertebrates, algae species, plant growth and all other life that combine in food webs with these.
We/humans haven’t died off because we feed from an artificial nutrient enhanced food source and not a natural food web.
Around the world scientists are confused as to what has caused such a decline because they research long term environmental chemistry changes or sample rainfall and surface water chemistry during high input events.
Silly people!!!
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They don’t research. I miss worded that.
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1) Insects aren’t really that important. People have assumed that they are, but well, if they’re going away en masse and it isn’t having much of an impact, perhaps not.
2) Ecosystems aren’t actually very fragile. There’s a huge amount of evidence for this; life finds a way, as they say.
3) The species that are going extinct are mostly the least adaptable species which fill the fewest ecological niches, which is why they’re going extinct in the first place.
4) Humans are much better at surviving than insects are; the biosphere is becoming more suitable for humans and less suitable for insects.
5) Obvious possibility: we’re miscounting insect decline. Given our estimates for the global biomass of insects vary by an enormous amount, I wouldn’t feel very confident in our numbers being reasonable or meaningful. It’s possible that, for instance, counting under different conditions gives wildly different results, and they just didn’t recognize that the conditions were different when they did the count.
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