It’s all the media rage just now, a rather modest metadata study that warns rather immodestly of an impending collapse of all insect populations within the next (human) generation. Stories about Armageddons are hard for reporters to resist, even good science reporters, and that certainly seems to have been the case in the month or so since this latest paper came out.
The new analysis treads ground regularly explored by naturalist-writers — see for example The Moth Snowstorm — and by researchers looking at single species or single landscapes. What the authors of Pesticides and Pollinators: A Sociological Synthesis did was a literature search pulling a lot these one-off studies together and extrapolating from the result.
Here’s CNN breathlessly quoting the authors: “The conclusion is clear: unless we change our ways of producing food, insects as a whole will go down the path of extinction in a few decades,” they concluded.
Ed Yong, science reporter for The Atlantic, is not so sure. He writes in the 19 Feb 2019 issue: “The claim that insects will all be annihilated within the century is absurd. Almost everyone I spoke with says that it’s not even plausible, let alone probable.”
The problem with the current study, he says, is what’s always wrong with these studies: They’re ad hoc, piecemeal, and spotty; aggregating them together doesn’t suddenly make them better.
“When scientists have collected long-term data on insects, they’ve usually done so in a piecemeal way. The 2017 German study, for example, collated data from traps that had been laid in different parts of the country over time, rather than from concerted attempts to systematically sample the same sites. Haphazard though such studies might be, many of them point in the same dispiriting direction. In their review, Sánchez-Bayo and Wyckhuys found 73 studies showing insect declines,” he notes.
“But that’s what they went looking for! They searched a database using the keywords insect and decline, and so wouldn’t have considered research showing stability or increases. The studies they found aren’t representative either: Most were done in Europe and North America, and the majority of insects live in the tropics. This spotty geographical spread makes it hard to know if insects are disappearing from some areas but recovering or surging in others. And without ‘good baselines for population sizes,’ says Jessica Ware from Rutgers University, ‘when we see declines, it’s hard to know if this is something that happens all the time.'”
Manu Saunders on the blog Ecology is Not a Dirty Word succinctly unpacks the problems with the paper’s methodology:
- The authors use a very limited and selective search string (insect* + decline* + survey). This is problematic for a few reasons: (i) it will mostly find papers showing declines, not population increases or stability; (ii) the term ‘insect’ is too broad and will likely miss many studies focused on particular taxonomic groups (e.g. bees) that don’t use the word insect; (iii) ‘survey’ is just one term that could pick up long-term studies. Ideally, you would also include other terms that might pick up long-term data, like “long-term” “monitoring” “historical records” “population dynamics” etc.
- The authors only search one database. There are multiple databases of peer-reviewed literature. For a comprehensive review, and to ensure the widest coverage of literature, it’s good practice to search more than one database.
- The authors only considered “surveys that reported changes in quantitative data over time, either species richness or abundance”. This means that any study showing stability (i.e. no change over time) would have been discarded.
- The study is not systematic or a true meta-analysis, as claimed by the authors. This may be pedantic, but science is based on standards.
Which is not to say that the trend line for many insect species — especially butterflies, and especially in the developed world — isn’t worrisome. But these tales of impending extinction do little to suggest a path forward or actually unearth an underlying cause. We know from past experience (climate change, anyone?) that scary, apocalyptic exhortations do less to stimulate public response that measured, what-can-I-do approaches.
Just as we’re learning the solution to Monarch butterfly declines isn’t as simple as “plant more milkweed,” we’re left with few concrete actions — and that’s probably because each of the insects under review probably need a different response to recover. There is no magic pill. Like politics, all ecology — and ecological catastrophe — is local.