By Guest Author 09/04/2019 7


Tom Saunders

Studies on insect declines published over the last few years have thrown up some scary headlines. “The insect apocalypse is here” proclaims the New York Times, warning the pace of insect declines could spell catastrophe within decades.

It’s a grim picture, but how accurate is it?

In late 2017, European scientists reported a 75% decline in insects over the last 30 years. On the surface, an alarming find. But when faced with any scientific study, always check the methods.

The Europeans weighed insects caught in traps from two regions of Germany. But most of the sites were only sampled during one year. This didn’t stop the New York Times from describing the study as providing “exactly the kind of longitudinal data [scientists] had been seeking” to confirm fears about a global crisis.

Biomass in itself is problematic. Could part of the decline be explained by a difference in average body size, rather than number of insects? The weight of insects in your trap doesn’t tell you anything about the number of species, the abundance of individuals within a species, or what kinds of insects are increasing or decreasing in number.

Sphictostethus nitidus, the golden hunting wasp. Auckland Museum (CC-BY 4.0)

In late 2018 a similar study blamed climate change for a large reduction in insect biomass in Puerto Rico. The authors sampled their sites for a couple of years in the 1970s and a couple of years in the 2010s. Again, they relied on biomass so the important questions couldn’t be answered: were there fewer species? Were certain species less abundant?

In January this year, two researchers published a review in Biological Conservation, aiming to “compile all long-term insect surveys conducted over the past 40 years that are available through global peer-reviewed literature databases.”

They reported “rates of decline that may lead to the extinction of 40% of the world’s insect species over the next few decades.” News media took the study at face value, claiming all insects could vanish within a century.

Image CC-BY-NC 4.0 by Maurice | iNaturalist

Scientists immediately pointed out flaws in the study design (reviewed nicely by The Genetic Literacy Project). Flaws included searching a single database, Web of Science, with the following query ([insect*] AND [declin*] AND [survey]). This will only return studies containing these specific keywords, and most importantly, will only return studies mentioning a decline. The authors noted they only included “surveys that reported changes in quantitative data over time, either species richness or abundance”, meaning studies reporting stable populations were discarded. This is inconsistent with their stated aim and skews the data towards highlighting declines, instead of presenting the whole picture.

As you can see in the figure below, the study rests on data drawn almost entirely from Europe and North America. The single data points from China and Australia relate to managed honey bees.

Sánchez-Bayo and Wyckhuys, Biological Conservation © 2019 Elsevier Ltd

This closer scrutiny of the methods reveals the study does not show global insect declines, or provide evidence for mass insect extinctions within the next century.

Taken together, the ‘insectageddon’ saga shows what happens when we fail to place individual studies into their appropriate context, and in doing so forget how science really works. It’s a cumulative process: studies build on the work that came before them. Understanding the big issues takes time.

As a passionate entomologist, I love it when people are talking about how cool and important bugs are. The last thing I want to do is shut down any conversations about insects and biodiversity. But I’m also cautious about how science is framed in the media. Scientists currently enjoy a high level of trust and respect from the public, something we should value and defend by ensuring we communicate our work honestly.

Tom Saunders is an entomology PhD candidate at the University of Auckland.

This article was originally published on Tom Saunders’ blog


7 Responses to “Dissecting the Insect Apocalypse”

  • I agree with Tom that the so-called “insect armageddon” is pure fiction. Biomass declines (in some places) are consistent with declines in one or more larger species, but most insect species are tiny. Biomass declines are also consistent with declines in one or more tiny, but previously numerically dominant species, but there are too many options to conclude anything meaningful from a mere overall biomass decline. Maybe one or two key species are in decline, while others are up in numbers?

    The interesting issue from my perspective is that pretty much every scientist knows that a few studies don’t point to a conclusion of global proportions, and also that there are multiple alternative explanations (as I outlines above) for overall declines in biomass, so why all the “insect armageddon” hype? I suspect that scientists are hoping for the same sort of massive scale funding as has become available for climate change research, by creating another “doomsday scenario” to worry funders. I would really hate to see $billions wasted on countless studies all over the world investigating the fictional “insect armageddon”. The strategy would be one of creating hysteria unnecessarily and then hoping for a massive injection of funding to investigate the basis for the perceived “doomsday scenario”, most or all studies resulting from such funding would no doubt be “inconclusive” to some extent, for that is the nature of science, and so it could go on indefinitely, much like climate change research.

  • Some of the declines will be real, and of course we are losing species, but my main point is the methods used in these particular studies don’t justify the sensational media headlines they’ve spawned.

    I don’t share your view that scientists are hoping to cash in on a wave of conservation funding. I think the main reason for these headlines is a mix of journalistic fervour to tell a compelling (and alarming) story, and some big issues with how the scientists involved have communicated their work (and not just in the original papers). For example, one of the authors of the latest review mentioned here has consistently used alarmist language in media interviews. He also blames pesticides when asked about the causes, and calls for a switch to organic farming. This, despite the fact he found pesticides were the main factor for declines in only 12% of the studies he reviewed (and it’s unclear how they defined a ‘main factor’ when there were several mentioned). The Genetic Literacy Project link I provided has many other examples of the review authors interpreting studies incorrectly, or conflating opinions expressed in a study with fact.

    I think ultimately we do need more investment in some areas, particularly taxonomy and longer term monitoring. But these investments don’t have to be enormous to make a huge difference. We just need to ensure the monitoring uses appropriate, standardised methods, and doesn’t only occur in North America and Europe.

  • Well, using alarmist language is one common strategy for creating the sort of hysteria that might motivate funders to spend big on such an issue, so I think that my suggestion (I wouldn’t call it a “view”) is consistent with the facts. I’m not claiming that ALL scientists are complicit in the subterfuge! I’m just suggesting that we really do want to avoid a situation whereby some scientists use the media to create a fictional “doomsday scenario” which then becomes a funding sink. This may be a factor in what is going on here, even if it is more complex that just simply that.

  • The decline in insect populations impacts the entire ecosystem, and as NZ holds the unenviable title of having the most endangered species in the world, I am really surprised to read this article. The situation in Australia is equally heartbreaking: https://www.abc.net.au/news/science/2019-02-27/bogong-moth-decline-in-australian-alps/10850036
    I suggest that you look at the long term legacy of NZ’s use of pesticides – e.g. the application of DDT for 17 years after it was banned in the USA – despite its known impact on avian fertility. Also the impact of 70 years of the broad-scale application of aerial baiting and crop dusting on biodiversity. To say that scientists have overstated the loss of insects or is using this data for financial gain is an extraordinary claim.

  • @Justine Mary PHILIP

    So, you are an anti-pesticide lobbyist. That’s up to you, but please do not misrepresent the facts about insect decline to further your agenda. “NZ holds the unenviable title of having the most endangered species in the world” only because DoC incetivised the putting of as many species as they possibly could on their threatened species lists (which has several categories, “endangered” does not accurately describe all the categories) in order to secure massive ongoing funding for predator free initiatives. It is all a massive exaggeration. There is no ongoing significant decline in insects in NZ (a very few species are truly endangered, but that’s all).

  • Hi Justine, were you directing your comment at me or Stephen?

    If me, I completely agree we are losing biodiversity, and that the causes are numerous. My argument in the blog is that recent headlines are stepping far outside the data of the studies they are relying on. For example, the claim that 40% of insect species could be gone in a few decades, or especially that all insects could be gone in 100 years is certainly not supported by these studies or any others. I believe its important for scientists to be upfront about the limitations of their work, and for media to resist the temptation to embellish their conclusions.

    As a passionate entomologist myself, I love seeing people talking about the importance and wonder of insects. But I think the way this research and media attention has been handled is a bit irresponsible. I would have been more comfortable if the review acknowledged the very limited scope of studies being looked at, and didn’t try to draw global conclusions from a (very patchy) dataset derived almost exclusively from North America and Europe. The link to the Genetic Literacy Project contains several other examples where the authors of the recent review made important errors in their interpretations of the studies they were looking at.

    In saying all that, yes, we absolutely need to establish standardised, regular, geographically widespread monitoring to spot any long term trends. And I’m especially in favour of investing more in taxonomy to describe all of our unknown species. I suppose my main point is that I worry the kinds of episodes outlined above may do more to harm public trust in science, and therefore harm the prospects of carrying out the high-quality research we desperately need. If people are shocked by bold headlines, but then see other scientists pointing out flaws in the methods, they may come to resent that roller-coaster. I worry science may become associated with hype a bit too much, to make people less likely to take scientists seriously, and less likely to support investment in science. I understand not everyone will share the same fear, but I hope you can see where I’m coming from.

  • Funnily enough Tom, I think your worry is unfounded: investment in science increases with media hype (which is why scientists seek out publicity), and what people do or don’t take seriously doesn’t enter into the equation.