Insectastrophe

Are the recent reports of insect numbers plummeting a dire warning or isolated phenomena?

You may have read about the observed declines in insect populations around the world. Many newspaper articles have claimed we are heading for ecological collapse and this has left me quite disturbed. The apocalyptic headlines stem from a couple of studies documenting dramatic declines in insect populations in protected ecosystems and indeed these are worrying. One study looked at trends across 65 nature reserves in Germany and found that since 1989 there has been an 82% decrease in flying insect biomass. Another study at a national forest in Puerto Rico found a loss of 98% of ground foraging, insect eating anthropods from 1976 to 2012. We’ve also heard about plummeting numbers of wild bee colonies and monarch butterflies. Are these declines ubiquitous or isolated?

The wikipedia page on “Decline in insect populations” starts with the following: “Several studies report a substantial decline in insect populations. Most commonly, the declines involve reductions in abundance, though in some cases entire species are going extinct. The declines are far from uniform. In some localities, there have been reports of increases in overall insect population, and some types of insects appear to be increasing in abundance across the world.”

Reading that, we might conclude that insect declines are balanced, or nearly so, by insect increases. That didn’t sound right to me. On top of the declines noted above are other trends which support the position that insect numbers globally are falling. Extinction rates are estimated to be 100 to 1000 times that of the fossil record. The number of wild animals on the planet has decreased by around 60% since 1970 and the biomass of wild mammals has fallen by 82%. A major driver in these decreases of wild populations is habitat loss. We’ve farmed over 50% of arable land and only some 25% of land is now considered wild. Arguably even the 25% of wilderness is no longer pristine wilderness given the global reach of climate change and the ubiquity of plastic particles. Considerations like these led me to doubt the opening paragraph of the Wiki entry.

I started digging into the research and found the story is not so clear cut as “Run for the hills” or “Everything’s just fine and dandy”. The story is more complex than either the headlines or the naysayers would have us believe, an emergent theme in these newsletters. There are a number of studies that conclude that insect numbers are falling. In addition to the 82% decline seen in Germany and the 98% drop in Puerto Rico nature preserves, listed above, are:

• All IUCN (International Union for Conservation of Nature) insect species for which there is documentation show an average decline in population of 33%.

• In the Netherlands and Switzerland, butterfly counts have declined by 84% from 1890 to 2017 and insect eating birds have declined by 60% since 1990.

• A review of 73 long term insect studies in the U.S. and western Europe shows a 2.5% decrease, every year, of insect biomass. The authors estimate that we may see an extinction of 40% of the world’s insect species in the next few decades. ***

• In 2018, only 14% of western monarch butterflies were observed relative to 2017. This could be due to wildfires and late season storms. A longer term decline of a 99.4% of butterflies since the 1980’s is more likely due to habitat loss, pesticides and climate change.

• Spikes in the collapse of wild honey bee colonies is potentially linked to pesticides. The pesticides in question, neonicotinoids, have been observed in wild bee populations and are known to disrupt bee behavior. The European Union has banned the suspected pesticide but the US has not.

So that’s a lot of different species and places suffering.

On the other hand, there are a few articles which find little evidence of an overall decline of insect numbers. A meta-analysis of 166 long term studies *** found that while terrestrial insects have declined by 9% per decade, freshwater insects have increased by 11% per decade. The increased number of freshwater critters may be due to efforts to reduced water pollution. And a new pair of studies by Crossley et al examined all the long term ecological research stations in the US *** and a citizen science database of butterfly observations. Both of the Crossley studies found that on aggregate there was no net change in US insect numbers. However, some sites experienced large insect declines (dry and hot sites) while relatively cool and moist sites showed moderate increases in insect numbers. This suggests that climate change is driving these trends.

So what’s going on globally? First, we have to be cautious about the conclusions of the global-scale-multi-species studies, marked above with ***, because there has been a good deal of criticism leveled at them from other scientists. Second, there are some winners and some losers in the insect kingdom. And third, although there is a mix of results, there is a strong consensus in all the studies I read that the status of the world’s insects is a serious cause for concern. There are places where insect numbers have plumetted. Monitoring and deeper studies are urgently needed as we know so very little about most insect species and what is known is geographically limited. Many of the studies call for changes in land management practices such as setting aside areas for wildlife and reducing pesticide use. There is also evidence that turning our lights out and drawing our curtains may be helpful for many insects die when they cluster around our lights.

In conclusion, while still concerned, I am far less panicked than I was before I wrote this article. The dramatic declines seen in Germany’s and Puerto Rico’s protected areas, don’t seem to be evident in the US and much of western Europe. One explanation may be that precipitous drops weren’t observed in these meta-studies because these areas experienced massive insect drops prior to the studies’ timeframes and have since leveled off. Such leveling off, and indeed even insect increases, have been seen in some of the datatsets and are typically attributed to land management choices like leaving wild strips on the sides of fields, reducing pesticide use and less farm expansion. Insect numbers leveling off is far better than a continuing downward spiral. What’s more it’s very encouraging to find that we can make positive impacts through our practices. Of course the dramatic declines need to be understood better - but a full scale collapse of insects populations doesn’t appear to be looming. When I told my son what I was writing about he commented, “That’s good news.” and I was startled to find that I agreed with him.