Moth populations

To my mind, this seems like a thorough study. Very concerning.

Of course this is “casual” evidence (Gulf Coast United States), but some of the local enthusiasts on moths/caterpillars in general have remarked on the lower numbers of them to be found this year over the last 3-5 years.

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Insects often have very fluctuated numbers, this year there’re 100 and second there’s 2, but next one 100 again. Also it depepnds on ecotope changes, e.g.Parnassius apollo population in Moskow region completely dissappeared mostly just because of vanishing its host plant species Sedum from places where it was found before.
That’s also well illustrated by the graphic from that German study.

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Thank you all for a warm welcome!

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of course, @boguo, we hope to see more of you on the forum :)

And another welcome to @michael64!

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Thanks. That’s kind of what I was looking for - more anecdotal evidence from the people doing the collecting. They would be the ones best able to give an overall sense of what is possibly going on.

And Welcome!!

Butterfly monitoring in the UK:
https://www.ukbms.org/docs/reports/2018/UKBMS%20Butterfly%20Annual%20Report%202018%20Low%20res.pdf

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Thank you for that. On first reading, very interesting!

I feel the ‘insect apocalypse’ narrative has been blown out of proportion.

Yes, biodiversity is inevitably declining as a result of human impacts. But that German study linked above, plus another one from Puerto Rico, and a review published last year by authors from an Australian institution, have been used to justify conclusions that step far outside the limits of their studies.

First we’re talking biomass, i.e. tipping out traps and weighing the bugs inside them. We’ll never know which species are going up or down from that data, or if the species themselves are invasive/native. Most of the sites in the German study were only sampled once, and the Puerto Rico data came from sites sampled multiple times but with decades between sampling events. This means we have no idea what the trend is. Were these sites sampled in trough or peak years?

The review published last year was host to a litany of basic errors in methods and interpretations. The lead author made very strong comments to the media which were not supported from the results of his work at all. Even the title (Worldwide decline of the entomofauna: A review of its drivers) is misleading. Practically all of the studies included were from North America or Europe, places which don’t contain the majority of insect diversity or abundance. Frustratingly, this review has become the “must-cite” source for introducing the topic of insect declines now, and will probably be uncritically parroted in most new papers.

Anyway, to answer your question more specifically, a rigorous, standardised, long-term moth sampling study from the UK (in which sampling occurred every year for 50 years) showed moth biomass to actually increase 2 fold between the first (1967–1976) and last decades (2008–2017) of monitoring. Study here: https://www.nature.com/articles/s41559-019-1028-6

The key thing to note from this study is the extreme variation in abundance between years.

Again, this is biomass so we can’t draw reliable conclusions about whats happening with different species, but at least this study gives a solid look at biomass. We need more proper monitoring of insects around the world if we want to uncover whats really going on. And we need higher resolution data - which species are declining, and where?

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Thank you. I do take all these studies with a grain of salt. I’ve been around science long enough to know that some things are just too difficult to quantify. Even medical research involving standardized matching and double blinding of groups produces dodgy results.
That’s partly why I was looking for anecdotal data - it’s possible to get a sense of what is going on with populations if you have enough observers. In my immediate area, American Robins have been hard to find in the past two years after 10 of abundance. Obviously, I can’t make a statement that robin populations are decreasing, but if enough observers around the city make the same observations, then a trend might be discernible.
Thank you for the link, and I’ll look at it later.

Just to be clear, I consider anecdotal evidence to be a form of Indigenous Knowledge (possibly opening up a new topic). I am not Indigenous, but know that Indigenous peoples have a long term knowledge of the lands they live on. If many people who have been hunting seals for decades say that they are more scarce now, then those observations should be considered. Not as quantitative science, but as a starting point for quantitative science (if possibe). I can tell you more about the river I go to every day than you probably want to know, but when it floods in the fall, that is a unique event, perhaps worthy of examination.

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I did a quick search on this topic and found this reference from Wikiwand: https://www.wikiwand.com/en/Decline_in_insect_populations. It reviews the studies noted thus far as well as a number of others. I agree that caution is needed in evaluating conclusions, but like you, I’m not a scientist, rather someone interested in science. Anecdotal evidence is often discounted, for sometimes obvious reasons, but if anecdotes are numerous, independent (i.e., not just repeating ‘common knowledge’) and consistent, then, it seems to me, they become a form of evidence worth paying attention to. The windshield splash test mentioned earlier is an example, as are comments from people finding fewer bugs at street lights or porch lights or realizing that we generally face fewer insects than many historical accounts describe. So, I really hope that insects are not in serious decline, but am concerned that they could be.

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From what professional enthomologists say fluctations happen all the time, some take years, but others need decades. Insects need environments, that’s what defining their future as group.

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And their environments are under threat, hence they are under threat…

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Well, the topic can be twisted as we want, but the windshield effect is there. At least for me in northern Italy. And speed limits have not changed much - and the difference when I was a kid and nowadays is tangible. I was the one who had to wipe.
And the heavy lobbying to hide all this is documented https://theintercept.com/2020/01/18/bees-insecticides-pesticides-neonicotinoids-bayer-monsanto-syngenta/
So I’d be cautious thinking of business as usual.

Once people hear an idea repeated often enough, such as “insect populations are declining globally”, they will, at first glance, interpret almost everything as supporting evidence for that idea. Only after deeper thought will other possible explanations come to mind. But most people will stop after the first glance, because nothing obviously contradicted the big idea, and deeper thought is hard work, to be avoided if possible. (Or, deeper thought is a limited resource, to be used only on the highest priorities.)

For example, the windshield effect. There are multiple independent observations from people who have noticed that fewer insects get splattered on their windshields now than in the past. At first glance, since insect populations are declining globally, the windshield effect is either obviously supporting evidence for the global decline of insect population, or the windshield effect is obviously an effect of the decline in global insect population (an important but often-neglected distinction, if you’re trying to understand what it all means). But one possible alternate explanation is that this is just evolution in action. Cars (and windshields) were invented about 100 years ago, and became common about 70 years ago. Insect populations being subjected to this new source of mortality have been evolving to avoid it, and this explains the reduced need to clean splattered insects off your windshields. You can see evidence for this when driving at night: your headlights reflect off of moths, and you can see them make a sharp upward turn as soon as they come into the beam of the headlight, when in the past they wouldn’t, and would end up splattered. (Note: this is just an example of an alternate explanation, one I’m not convinced is true. If you think on it a bit more, you may be able to come up with another possible explanation or two, for the windshield effect and for almost any other isolated piece of anecdotal evidence.)

For moth populations, the U.K. long-term studies are the best I’ve seen. I’m much more familiar with monitoring bird populations in North America, but there are a lot of parallels. The main thing is that one or two years of data are somewhat useless on their own. There are large changes in local and regional populations from year to year. The populations plotted over time don’t look like straight lines, they look like crazy zigzags which don’t tell you anything until you have 10 or 15 years of data, preferably 30 to 50 years. This is the sort of thing that’s meant when people say that anecdotes aren’t useful data. I expect the same thing is true of moth populations.

For example, the Monarch population where I live quintupled over the past two years, but this tells me nothing about the long-term prospects for Monarchs, because I live in Canada and the eastern North American population’s long-term prospects are almost entirely dominated by the conditions in their tiny wintering areas in Mexico. The low population here two years ago was almost entirely due to a severe winter storm there, and the quintupling of the population is simply recovery from that. Any long-term population trend requires data over a much wider spatial area (Monarchs have populations in Australia and Indonesia) and over a much longer time-span (decades at the least). And the specific circumstances affecting Monarchs don’t even apply to closely related butterfly species, much less to moths as a group.

In North American birds, we’ve found about 30% of species increasing, 30% stable, and 40% declining, and the total population declining slowly. Some few species have declined incredibly rapidly, while some few others have increased enormously (e.g. goose populations in N. America went up by ~400% between 1970 and 2010). The species going up in N. America are mostly those which are recovering from the DDT-caused crash in the 1950s and 60s and from past over-hunting. The species going down are mostly the ones which depend on non-agricultural grassland and those which migrate to South America. (I don’t know what’s happening down there, but something important is.) Overall, the total biomass of birds in N. America is declining slowly, i.e. <1% per year from 1970-2018. Compared to the year-to-year fluctuations, this is all but undetectable without really massive amounts of data. On the other hand, like all percentage-based changes it compounds quickly. The media inevitably quotes the most heart-attack-inducing number they can find, which in this case is “3 billion birds have disappeared”, while downplaying (or rather, failing to emphasize with equal force) that it happened over a 50 year period, and failing to mention the total population size. I don’t mean that birds aren’t declining, or that it isn’t important, but I’m trying to maintain a reasonably correct perspective, along with some healthy uncertainty about the true situation. Otherwise I might start thinking all birds will be extinct by the end of the century, which is nonsense.

For moths, the long-term U.K. moth records seem to show something similar: some species going up, others down, still more relatively stable, and an overall steady decline in biomass as wild lands get converted to agriculture to supply the increasing human population. Since this is not the kind of thing which grabs your attention, this is not what you’ll hear about most often in the news or in gossip. Real answers are always along the lines of “Well, it’s more complicated than that (and here’s how:)”, except when they aren’t (sigh).

Incidentally, I received a moth trap from Britain for Christmas. The bird observatories there have long been catching and recording moths in addition to their other activities, and I’m planning to experiment with doing the same at Long Point Bird Observatory. If that works out, then we might try getting the other bird observatories in Canada to do the same thing, so that in 20 years or so we have enough data to do a report like the one from the U.K. for Canadian moths.

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Absolutely, I agree anecdotal and indigenous knowledge can provide excellent starting points for the collection of quantitative data to provide a scientific view.

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People can and will argue in whatever way serves their worldview, but I’m far more interested in quantitative evidence collected over a long period of time. The situation is far more complex than “I personally don’t see as many bugs these days as I used to which means insects are declining globally.” My caution is exactly the reason why I’m suspicious of arguments put across without evidence to accompany them.

As a side note, whether or not chemical companies are hiding evidence that their products are causing bee declines is very different to whether or not insects as a group are declining globally. Putting the probable corporate wrongdoing aside, honey bees are not native to most parts of the globe, and in these areas they are essentially cows with wings, they’re managed livestock. They can easily outcompete native bees and other native insects. So their very presence in some areas may be contributing to the decline of native insects. They’re also not the only insects that pollinate crops or wild plants, and in fact, they’re probably not the most important group of pollinators for wild biodiversity. People tend to assume bee populations are a mirror to how nature is doing in general.

Theres so much nuance and complexity tied up in this topic and current reporting is simply not doing a good job of unravelling it and explaining it (and this is certainly not only the fault of the media when you have study authors and press releases embellishing their findings).

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Well, as an engineer I would rule out thinking that an insect (speed… 5-7kph, if we exclude dragonflies?) has evolved in 30 years to avoid an object travelling at 110 kph.
I’d be more ready to believe that car have a significantly improved Cx, but that happens with vehicles like buses as well. In any case the windshield effect is the most readily available hint - that has been a starting point in the Krefeld investigations I read about here , where long terms analysis is also mentioned, if you’ve some time to read it through I think is a good arcticle.

well, I’d avoid extremes and I’m no expert to talk about birds I just base on my irrelevant experience that in my area in Italy I cannot see the sparrows, partridges, and the like (I know it’s not statistics but again clue) I used to see when I was a child.
I’d be interested reading some studies focusing on insectivore birds. That would be interesting, but I have not found any.

By the way, Jeremy, from the link you have added I extrapolate that insectivore birds are the worst faring with -59%, what’s your view on that? I don’t think it’s helping to think business as usual in insect world.

Obviously as it always happen in the insect world i’m ready to think there can be exceptionn to a general trend (which I find quite reasonable, as functional extinction generate new niches where other insect can fit into), but I am trying to get a reasonable opinion which applies to the area I live in, taking in mind other points like the concept of functional extinction mentioned in the article of nytimes linked above
After all there must be a reason behind Council Directive 2009/147/EC and the Habitats Directive in EU
I am quite wary of the shifting baseline syndrome descrived in the article above
and of the brain tendency to deny problems which imply cost, future effects and uncertainty (you can listen to this podcast entry to understand what I mean)

of course. Totally agree. but I think in the end (I’m no scholar) but you have to build an opinion, and between the three options (situation improving/stable/worsening) I personally feel that worsening, all information collected so far, is the most reasonable opinion, based on the global studies available

Thanks Jeremy, your comment was a very good read.

see my reply to Jeremy.
I know very well that bees are just the cows of the insect world, and alloctone as a consequence, (btw I am for wild pollinators so figure it) but they are also linked to money interests, which is pushing some other people to analyze the impact of other industry practices on them and take action to protect their own money- that’s why I mentioned them

Honestly, I think no one would lift a finger to analyze the impact or fight neonicotinoid use just to protect bugs who do not directly generate revenue. That’s the way it is, especially outside Europe (and some small areas of India, I reckon) where unrefrained heavy lobbying by big industry is part of the way things work.
That’s why bees are the only reference for me to understand in some detail what’s up in the world of insects.

have you read the Krefeld study mentioned above? https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0185809

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Re the UK butterfly monitoring: It helps to know 1976, the year it began, was an exceptionally hot summer, a good year for adult butterflies, so the starting point for the index was higher numbers than in a more typical year.

Re splattering: I should think cars becoming more aerodynamic has some effect. Is that what Edolis means by improved Cx?

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