New Study Highlights Collapse of Insect Populations

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An important new study that finds a dramatic fall in the insect population in a protected tropical rain forest hasn’t gotten the attention it deserves. To its credit, the Washington Post appears to be the lone mainstream media exception. Its story, ‘Hyperalarming’ study shows massive insect loss, not only covers the new PNAS article, Climate-driven declines in arthropod abundance restructure a rainforest food web, but also summarizes other recent studies on insect populations that show similar alarming declines. And what is particularly troubling is that the new studies attribute the fall in insect numbers to climate change, not pesticides.

Google News shows only one other story on the PNAS study, Several species of insects have almost completely vanished from some tropical forests in Science Magazine. Two other articles discussed insects as food: INSECT CUISINE: HOW TO EAT (AND ENJOY) THE ENVIRONMENTALLY FRIENDLY SUPERFOOD in Newsweek and The ever-growing case for eating insects The Takeout. It looks like this idea may have arrived too late.

The PNAS study measures insect biomass over time in an isolated rain forest in Puerto Rico. The authors point out that insects in tropical settings are more vulnerable to changes in temperature than insect species that live in other habitats.

As the article title indicates, the plunge in insect numbers has devastated the species that feed on them:

Arthropods, invertebrates including insects that have external skeletons, are declining at an alarming rate. While the tropics harbor the majority of arthropod species, little is known about trends in their abundance. We compared arthropod biomass in Puerto Rico’s Luquillo rainforest with data taken during the 1970s and found that biomass had fallen 10 to 60 times. Our analyses revealed synchronous declines in the lizards, frogs, and birds that eat arthropods. Over the past 30 years, forest temperatures have risen 2.0 °C, and our study indicates that climate warming is the driving force behind the collapse of the forest’s food web. If supported by further research, the impact of climate change on tropical ecosystems may be much greater than currently anticipated.

A number of studies indicate that tropical arthropods should be particularly vulnerable to climate warming. If these predictions are realized, climate warming may have a more profound impact on the functioning and diversity of tropical forests than currently anticipated. Although arthropods comprise over two-thirds of terrestrial species, information on their abundance and extinction rates in tropical habitats is severely limited. Here we analyze data on arthropod and insectivore abundances taken between 1976 and 2012 at two midelevation habitats in Puerto Rico’s Luquillo rainforest. During this time, mean maximum temperatures have risen by 2.0 °C. Using the same study area and methods employed by Lister in the 1970s, we discovered that the dry weight biomass of arthropods captured in sweep samples had declined 4 to 8 times, and 30 to 60 times in sticky traps. Analysis of long-term data on canopy arthropods and walking sticks taken as part of the Luquillo Long-Term Ecological Research program revealed sustained declines in abundance over two decades, as well as negative regressions of abundance on mean maximum temperatures. We also document parallel decreases in Luquillo’s insectivorous lizards, frogs, and birds. While El Niño/Southern Oscillation influences the abundance of forest arthropods, climate warming is the major driver of reductions in arthropod abundance, indirectly precipitating a bottom-up trophic cascade and consequent collapse of the forest food web.

As Science Magazine put it:

Insects and other arthropods have declined by up to 99% over 4 decades in a Puerto Rican forest, apparently because of climate change, according to new study. And that’s not the only bad news….

Something similar happened in the Chamela forest of Mexico when the two researchers compared the abundance of arthropods in 2014 with their previous survey in 1987–88. Meanwhile, the average maximum daily temperatures in the Puerto Rican forest have risen 2°C, and by 2.4°C in the Mexican forest. Ecologists know excessive heat can harm animals, especially those that have evolved to live in relatively constant tropical temperatures.

The Washington Post pointed out that the (few) other studies on insect population have had similar grim findings:

Insects around the world are in a crisis, according to a small but growing number of long-term studies showing dramatic declines in invertebrate populations. A new report suggests that the problem is more widespread than scientists realized. Huge numbers of bugs have been lost in a pristine national forest in Puerto Rico, the study found, and the forest’s insect-eating animals have gone missing, too.

In 2014, an international team of biologists estimated that, in the past 35 years, the abundance of invertebrates such as beetles and bees had decreased by 45 percent. In places where long-term insect data are available, mainly in Europe, insect numbers are plummeting. A study last year showed a 76 percent decrease in flying insects in the past few decades in German nature preserves.

“This study in PNAS is a real wake-up call — a clarion call — that the phenomenon could be much, much bigger, and across many more ecosystems,” said David Wagner, an expert in invertebrate conservation at the University of Connecticut who was not involved with this research. He added: “This is one of the most disturbing articles I have ever read.”…

The food web appears to have been obliterated from the bottom. It’s credible that the authors link the cascade to arthropod loss, {Louisiana State University entomologist Timothy] Schowalter said, because “you have all these different taxa showing the same trends — the insectivorous birds, frogs and lizards — but you don’t see those among seed-feeding birds.”…

A recent analysis of climate change and insects, published in August in the journal Science, predicts a decrease in tropical insect populations, according to an author of that study, Scott Merrill, who studies crop pests at the University of Vermont. In temperate regions farther from the equator, where insects can survive a wider range of temperatures, agricultural pests will devour more food as their metabolism increases, Merrill and his co-authors warned. But after a certain thermal threshold, insects will no longer lay eggs, he said, and their internal chemistry breaks down….

Lister [one of the co-authors] pointed out that, since 1969, pesticide use has fallen more than 80 percent in Puerto Rico.

Readers have been pointing out that they can tell there are fewer insects. A long highway trip no longer produces a windshield crudded up with dead bugs. Even in concrete-heavy Manhattan, I’ve noticed that the usual few flies that manage to make their way up the elevator and into my apartment during the summer, much to the delight of my cats, are a thing of the past. When I go to outdoors-y places during mosquito season, I get a fraction of the number of bites I used to receive.

Cockroaches may inherit the earth, but it looks like it’s dicey to bet on anything else.

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  1. kimyo

    Lister [one of the co-authors] pointed out that, since 1969, pesticide use has fallen more than 80 percent in Puerto Rico.

    it would be helpful to know if, alongside the decline, a switch to more-toxic pesticides took place. here in new york, there are things on the shelf at home depot which weren’t commonly available in 1969.

    1. Yves Smith Post author

      Yes, that’s what the study said: “…our study indicates that climate warming is the driving force behind the collapse of the forest’s food web. If supported by further research, the impact of climate change on tropical ecosystems may be much greater than currently anticipated.”

  2. Bob


    If the insect population is collapsing as it appears to be as a result of Global Warming we are headed to another silent spring.

    In fact perhaps we should reread Rachael Carson’s classic and then after winter is over listen to see if the birds dawn chorus is diminished as it appears to be here in the Carolina’s.

  3. nervos belli

    The cry “it’s global warming!” is imho a very stupid one here. What has changed due to AGW in tropical rain forests? It’s suddenly steppe or desert? Has the rain fall lessened dramatically? Do more hurricanes kill off all the insects?
    No it’s still rainforest, whatever rain forest is actually left.
    Even if it is global warming, wouldn’t the insects simply migrate to the Florida swaps or the formerly cold steppes of Canada? Billions of mosquitoes there then which would make it basically a wash regarding biomass?

    The reasons are probably very different: population density, pesticides + mono cultures, intensive land use for economic gain, etc. Simply: more humans who want to exploit more of the earth.
    1970 there were 2,7 million inhabitants in Puerto Rico, to a maximum of 3,8 million and now 3,3. My guess is a lot of rain forest from the 1960 simply doesn’t exist anymore, especially “old growth” forest.
    The GDP went from ~4 billion in 69 to now 100 billions.

    1. Yves Smith Post author

      You are really asking to be boxed around the ears. Your comment is in a category of stupid all of its own. And you clearly didn’t read the post in full, which is a violation of our written site Policies.

      The article states:

      Meanwhile, the average maximum daily temperatures in the Puerto Rican forest have risen 2°C, and by 2.4°C in the Mexican forest.

      Thats a huge increase and the paper also states that tropics insect species were expected to be more sensitive to temperature changes than other types of insects. Did it not occur to you that insects don’t regulate their internal temperature like mammals do and don’t wear clothes to help do that either?

      Second, the idea that insects can migrate is absurd. They are adapted to their local environment. Insects are not migratory birds who navigate using magnetic fields. They can’t fly far either. And how are they supposed to have the idea that there could be a better place across a long expanse of ocean with high winds and no food? Do you posit that they go on the Internet, figure out that maybe they can survive in Florida, and book a flight?

      Third, the article very clearly explains that these were pristene rain forest, well protected, and the pesticide level in PR is vastly lower than previously measured levels.

      I should not have to waste my time debunking dopey claims that reflect your refusal to read.

      1. kimyo

        temperature changes in nyc, though, are much more modest and seem less likely to be the cause of the decline in local insect populations. nyc warmest/coldest months (pdf)

        in central park, the warmest month recorded was july 1999 @ 81.4f, with july 2010 following close behind at 81.3f. however, previous records include july 1955 (80.8f), july 1952 (80.3f), july 1908 (80.1f) and july 1949 (79.6f).

        the difference between july 1908 and july 1999 is only 1.3f.

        from a cui bono perspective, the biggest beneficiary of this study is bayer/monsanto.

        the other thing that ‘bugs’ me? it’s the hottest areas on earth (australia, africa) which have the largest insect populations. over the long run, it seems that more heat equals more insects.

        1. pretzelattack

          from the study
          A recent analysis of climate change and insects, published in August in the journal Science, predicts a decrease in tropical insect populations, according to an author of that study, Scott Merrill, who studies crop pests at the University of Vermont. In temperate regions farther from the equator, where insects can survive a wider range of temperatures, agricultural pests will devour more food as their metabolism increases, Merrill and his co-authors warned. But after a certain thermal threshold, insects will no longer lay eggs, he said, and their internal chemistry breaks down….

          Lister [one of the co-authors] pointed out that, since 1969, pesticide use has fallen more than 80 percent in Puerto Rico.

          insects, like other animals, evolved for a certain range of temperatures. this study focused on insects in tropical rain forests, but i’m not sure why it wouldn’t apply to insects in other areas.

          the rate of warming is supposed to increase as we continue to fail to address the problem, although that will vary across the globe.

        2. Yves Smith Post author

          I didn’t make the NYC observation about declining insect populations in the comment above. The post refereed to several studies showing falling insect numbers. The tropical ones that concluded climate change was the big driver were the most prominent but not the only ones.

          Please don’t act like you are defending an idiot by placing a comment in the wrong spot.

        1. Code Name D

          There is nothing like a girl weilding the giant anime pan-dimensional hammer of truth.
          Bam! Sqush! Nothing sexer. (@ @ )

          Reason enough to donate. (operators are standing by. (^_^ ) )

      2. Bruce F

        Your comment is in a category of stupid all of its own.

        This made me laugh. It was on my mind as soon as I read the original comment. Thanks! For what it’s worth, your response is what finally pushed me into making a (small) donation.

        NC is a place I keep coming back to.

        Thanks again to all who keep it going.

  4. fresno dan

    I commented a few weeks ago about the lack of earthworms and butterflies in my garden. I told you so!

    1. juliania

      This would be a good time to advocate a trick I’ve been using the past few summers – if you have a garden, don’t throw away those gallon pots (plastic :( ) sitting on the garage shelf – put them out in that overheated garden any empty spot and as your trees, shrubs, flowers and veggies throw off leafage more and more these summers, use those pots as miniature compost heaps. Then each morning, check underneath – there will be slugs (which I chuck up on my metal roof to let the sun fry) but there will also be worms that come up into your compost each day/night to forage. Leave the tubs in place and gradually the worm castings accumulating beneath them will renew your soil. Add leafage from fall and from clipping back your happier shrubs, kitchen compost too. Win-win!

      Never put fall leaves in the garbage. Your tree needs them; the soil needs them. Compost!

  5. JCC

    Last year I planted a few blooming plants to attract/feed butterflies and others here in the North Mojave and was happy to see a few Painted Ladys and Monarchs in the yard feeding in the plants. This year, more plants, more flowers, and I would walk around often looking for good results, but not one butterfly seen.

    And again, a vacation in Upstate NY in August, clean windshield, no lightning bugs, and I think I got a mosquito bite or two, but I can’t really recall any.

    Anecdotes might not be evidence, but it still makes me more than a little nervous. In fact, it’s starting to get frightening.

    1. Lord Koos

      We are experiencing a great extinction event but so far it’s been mostly insects and sea life. It may take awhile, but humans and other mammals at the higher end of the food chain will be next. Interesting times indeed.

      1. blennylips

        We’ve only recently gotten around to noticing the small, out of the way life forms.

        Seemingly it did not take long to eat all the mega fauna as the last ice age retreated: From the top, working our way down.

        Now, after the last fifty years?

        Most of the Mammals On Earth Are Cows Because We’re Addicted to Meat

        A new study of all the biomass on the planet found that 60 percent of all mammals are livestock.

        Humanity Has Killed 83% of All Wild Mammals and Half of All Plants: Study

        Of all the birds left in the world, 70% are poultry chickens and other farmed birds.

        Lord, it is hard to see how humans, driving this mass extinction, could do more than they already have.

    2. Yves Smith Post author

      Yes, I neglected to mention how few lightening bugs I saw when I happened to be in Alabama at the right time. When I was a kid, we lived in the panhandle of Maryland for a bit, and the back yard would be full of them. It was easy to catch enough to get a bunch in a glass bottle, where they’d blink on and off together.

  6. Webstir

    I’m noting my emotional reaction to this post as I type.
    I don’t think it can be described as anything other than depression.
    Which, since depression tends to pull us inward, seems a terrible evolutionary response to crisis.
    As an alcoholic in recovery, I well understand that our emotional well-being depends on our actions — not our thoughts.
    Listening to non-adaptive thoughts leads to an emotional race to a cognitively dissonant bottom.
    Thus the old AA saws: “fake it ’til you make it,” “feelings aren’t facts,” and “ACT as if”

    I’d be very interested in hearing about people’s emotional response to this post, and how they go about coping.

    1. freedomny

      I cried. But then, I do that a lot these days….

      And I’m coping by trying to make plans for the future that involve completely changing…..pretty much everything.

    2. Bobby Gladd

      I’ve been reviewing the IPCC Report and the activities of various organizations involved in remediation / sustainability research, world-wide. I too am fighting off being depressed by the increasingly dispositive evidence of the exigent circumstance we face. Seven weeks out of open heart (aortic valve replacement) surgery (mere months after losing a 2nd daughter to cancer), my shaky coping of late is limited to studying and posting about the issues (I’ll be adding this PNAS study). The intransigent Trumptocracy / GOP Denial leaves me at a loss as to what more to do personally.

      I recently finished James Alcock’s excellent 640 pg book “Belief,” which I commend to everyone. Sheds detailed light on the sources of intractable denialism (i.e., the neuropsychology of human cognition).

    3. Lord Koos

      At one time I often became very depressed after reading these type of findings. After a certain point I realized I have no control over what is happening and that worry and depression isn’t going to help anything. The earth will survive, and species will someday replenish and evolve in adjustment to a hotter environment. We may not be among the species that make it, of course… humans are clever but not very wise.

    4. JCC

      Just plain sad. And concern about my own future, of course, as in how to go about effective long-term planning.

      But overall, as Lord Koos says using other words, the Earth Abides. What the heck, it was a good run for those that learned how to appreciate what really matters.

    5. Jeremy Grimm

      In response to this post and numerous other readings on Climate Disruption and Peak Oil I’ve been growing increasingly depressed. I’ve been drinking more than I should. I’ve lost my drive to accomplish even simple tasks. Little problems that come up depress me all out of proportion. I am losing the faith I can do something meaningful or helpful to my family with the resources available to me and in the years I have remaining.

  7. Polar Donkey

    17 years ago, Saturday nights at south pole station, scientist would do presentations on their research. The climate scientists were scary, but what they said was still in the future. The future is now. I look at my 2 and 4 year old boys and worry. It has been awhile since I have been around research scientists. Seeing their subject matter first hand, do they still have children or are they losing hope?

    1. paleobotanist

      Some of us have chosen not to have children for that reason. It doesn’t really help though, we still have students you see, who are our children. And I just found a nephew this year. So you see, we’re still committed to the future, regardless.

  8. Shilo

    I wonder if anyone has looked into the huge success of ivermectin anthelmintics (wormers), potent in microgram doses, in totally disrupting the parasite life cycle, by poisoning even the larval stages. Passed out in the feces, it’s loose in the environment. It’s been many many years since I’ve seen bot eggs on the legs of a horse or a pile of cow flop covered with manure flies.

  9. Jean

    Pesticides are biocides. They should be banned. Period.
    Those who claim their safety should ingest a few drops of them in a glass of water in a public forum to show their convictions, or better yet, have their grandchildren drink the mixture, then we’ll believe their sincerity, but perhaps not their scientific accuracy.

    Anyone with even the smallest yard can take the time to learn what plants favor local insect and their predators’ life cycle and then do something with a trowel and a few dollars worth of plants inserted in the ground.

    Just doing nothing as far as maintenance is favorable to insects and birds as ‘trash’ creates habitat that no lawn can. Oh, and if you like birds, put a bell on your cats.

  10. JerryDenim

    I don’t disagree with the main thrust of the article, and I don’t doubt climate change can have catastrophic effects on rainforest insect populations, but I have some serious doubts about choosing Puerto Rico as subject due to “minimal”pesticide impacts. Puerto Rico is a tiny little island (hard to isolate anything there) that for many years has been cruelly used as a testing ground for pesticides and chemicals deemed too dangerous for the mainland USA. The military, the USDA and big agribusiness corporations like Monsanto have all been involved in toxifying the island and it is still happening today. Puerto Rico’s rainforests ( basically one small area around the island’s one distinctive volcano/mountain ) were the main testing grounds for the famously toxic and long lasting poison Dioxin – a.k.a. Agent Orange.

    1. Tom67

      Thanks Jerry. I believe this article is fishy as well. Against:
      _There are thousands of insect species and some would definately profit from a change in temperature. Biodiversity should decrease (which is very bad in itself) but biomass not by that much.
      – There have been climate swings just as bad in the past. Just think about the little age ice age in Europe in the 15th and 16th century.
      As long as I don´t see a part of the world non effected by chemicals having the same observations I very much doubt that the decline in Puerto Rico is down to climate change. In fact I lead wilderness tours in Central Asia and our clients from the rich West are always flabbergasted by the amount of insects that are attracted by their lights. This summer I remember that just one light attracted such a mass of incects that we had to stop eating. When I told the person wearing his LED heand band to turn it off it all stopped. Now imagine what terrible effect all the articial light is having in the industrial world.
      I think it It leaves out much more important points. I live in Germany and here the decline in insects is truly dramatic. But nobody here believes climate change is the important driver. It is a myriad of things connected with our lifestyle:
      – Light. Light. Light. All nocturnal insects are effected by this to a truly staggering extent.
      – Compounds of chloride and carbon. There are tens of thousands of them (think Phtalates) and the most widely used turn out to have deletirous effects. They are then replaced by supposedly safer ones which are again shown to have dangerous effects. And so on and so.
      By the way: I am also a bee keeper and all this is not controversial among us.

      1. Webstir

        Let’s assume both of your arguments contain truth.
        The fact is, we are changing the world so fast the science can’t keep up.
        Fishy, or not. It’s happening.

  11. Tomonthebeach

    The reaction from folks at Bayer-Monsanto? Great, our poisons are working!

    The PNAS article makes assumptive leaps when discounting the B-M effect. Weather moves manmade toxins around. Assertions that these toxins have short shelf lives and are thus not important factors is laughable.

    Forces that might contribute to the drop in insect populations:

    – Insects have shorter shelf lives than DDT, Roundup, etc.
    – Torrential rain runoff disperses toxins – even into rainforests
    – Bugs are not stationary beings – they migrate.
    – Hurricane-force winds migrate bugs involuntarily (on islands like PR wind can move rainforest bugs out to sea where there is no food)
    – Hurricane-force winds also destroy vegetation for food and reproduction

    This last point requires surviving a hurricane. After Irma, for example, every leaf on our shrubbery was stripped off. It took 6 weeks to sprout again.

  12. nippersdad

    This is, indeed, very depressing. However, anecdotally, I have seen a large uptick in the sales of native plants the past few years; a lot of people appear to be getting it.

    Something that I read recently, Bringing Nature Home by Doug Tallamy, really gave me cause for hope. It is a great book, written with the average homeowner in mind, that breaks down the kinds of issues behind the loss of our arthropod communities and how to get them back. Well worth the read, IMHO.

      1. nippersdad

        I saw that and plan on getting it. I’m presently working my way through the plant lists in Native Plants of the Southeast by Mellichamp and Stuart, but additional native plant lists are always a welcome addition.

        One really doesn’t think about the number of exotics one puts out, and I find that my former reliance on Dirr wasn’t much of a help, so landscaping with native plants is a fairly new challenge for me. I am finding that those plants that haven’t been eaten are sticking out a lot more these days and, for many of them, it has me questioning why they need to remain.

  13. Synoia

    I went to the west Coast of Costa Rico in 2012, and stayed at a resort newly developed.

    It was hot and humid, but there were no bugs at the resort, Riu Guancaste, nor in the neighboring town of Playa Hermosa. The wildlife was sparse, even on the rivers through the Parks,

    My expectations, lived in Nigeria as a child was to expect swarms of bugs, many lizards and many birds. But I had no baseline to make an observation, so I cannot make any comments based on a change.

    The wildlife in no way matched what I experienced from my childhood in Nigeria.

  14. Wukchumni

    I tend to notice bothersome insects more than anything else, and there was no shortage of mossies and biting deer flies this summer in the higher climes of the Sierra Nevada.

  15. KPC

    This article is OK as far as it goes.

    It has long been known that two of the primary culprits of this mess are insecticides and herbicides. Of course, global climate change adds to the problem. Tis a circle.

    The first thing we need to do now and long ago is stop using insecticides and herbicides.

    If one is interested, Rachel Carson’s book in full is available in pdf format with no charge here: . I have not read it in years. It was published in the 1960s.

    As for you people up north and the rain forest stuff, you have responsibility to fix your zone now. We are working to fix our zone in middle earth with no need for endless lectures and worse from outsiders who have caused a disproportionate portion of this entire problem.

    A really big part of the solution is each and every one of us must change our behavior now.

    From an attorney, accountant and diplomat in middle earth with family in the same professions and medical in the north and here as well.

    Buck up. Get back to work.

  16. VietnamVet

    The fireflies and honeybees are gone from my suburban Maryland home. The swarming of tiny insects around street lamps is nearly non-existent. The few remaining self-pick strawberry fields are miles away. Science is how mankind would discover the reasons for this and similar observations. What is scary is the retreat into denial and fundamentalism. The major party of the USA that controls everything except six coastal states is anti-science. The Environmental Protection Agency is being dismantled. Bayer will not fund serious extensive pesticide field studies on the effect of neonicotinoids on non-target organisms for the same reason Volkswagen fudged diesel emission tests. The truth hurts their bottom line.

    One also can observe that the ruling elite treats the little people like pests.

  17. Ping

    For several years I have noticed it is uncommon to see an insect (Tucson). I don’t see ants, grasshoppers, very few flies or bees or anything else. Almost never a bug on the windshield.

    On lovely spring days this year, there were very few birds chirping, a silent spring and a harbinger.

    I attribute it to environmental toxicity.

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