The effects of climate change may already be evident in our changing insect populations. Image credit: James Wainscoat via Unsplash
Back in 2017, a landmark study sent shockwaves through the ecological community by reporting a staggering 75% decline in flying insect biomass in Germany. Now, a new report has demonstrated that these changes in abundance were linked to the weather— showing that climate change could be impacting insects in temperate zones sooner than we thought.
The ‘Insectinction’
We are facing an ‘Insectinction‘. Globally, over 40% of insect species are in decline, at a rate that is almost 8 times faster than other groups of animals. Whilst this may come as a relief to some entomophobes (people who are afraid of insects), scientists have every right to be worried. Insects are the most diverse group of animals on earth, with over 1 million species described. They also provide us with a multitude of essential ecosystem services, including pollination, nutrient cycling, and pest control—much of which underpin the agricultural industry. For example, cow-pat eating dung beetles are estimated to be worth £367 million a year to the UK cattle industry alone, with pollination services valued in the hundreds of billion dollars annually worldwide. In addition to helping produce much of the world’s food, insects themselves are an essential food source for animals and humans in the 80% of the world’s nations, where insects form a staple part of the diet. They form complex, mutualistic relationships with the flora and fauna around us. Without insects, we risk losing many other species and our ability to feed the planet.
We are facing an ‘Insectinction‘.
There are many factors driving insect declines, including habitat loss, insecticide and herbicide use, invasive species, and climate change. In the UK, we have lost over 97% of wildflower meadows since 1930 and 87% of wetlands, both of which are vitally important habitats for insects. Amongst these drivers, climate change is often ranked as “least important”. This particularly applies for temperate zones, where climate change is expected to increase the abundance of insect populations through range expansions and increases in reproductive rate. Nevertheless, such effects are likely to be species-specific. A 2021 study of arthropods in North America showed worrying declines in abundance when researchers artificially raised the temperature of their natural habitat using heated chambers. And of course, climate change does not just imply global warming: it involves complex changes to a whole host of weather events including precipitation, humidity, and even seasonality at a large scale. Despite this, few studies have attempted to investigate how combinations of weather conditions might actually be affecting insects in the real world, until now.
Few studies have attempted to investigate how combinations of weather conditions might actually be affecting insects in the real world, until now.
A historical dataset analysed in a new light
The report was led by Professor Jörg Müller and his team at the University of Würzburg in collaboration with the Technical University of Munich and University of Zurich. Published in Nature in September 2023, it reanalyses a dataset of flying insect biomass collected from over 60 protected sites across Germany over a 27-year period between 1989 and 2016. By incorporating sample–specific temperature and precipitation data into models of varying complexity, the team attempted to deduce what exactly was driving the variation over time in insect biomass. They tested models containing different combinations of variables, including season, habitat, sampling year, and finally, weather conditions. Their results were striking—the model including weather conditions explained roughly 75% of the variation in biomass seen, even when the sampling year was removed. Therefore, they concluded, temporal changes in weather conditions were likely to be driving the changes in insect biomass observed throughout the study period.
What is even more interesting is that in Germany, insect biomass had increased in the five years since the 2017 study was published. Yet, the authors found that weather conditions explained both this increase and the decline that was previously observed over a decade between 2005 and 2016. Looking further, the authors found two specific combinations of adverse weather conditions that were driving abundance changes. Warmer, drier winters were associated with reductions in biomass, likely due to negative effects on overwintering insects such as butterflies and beetles. Meanwhile, hotter, wetter springs were linked to increased biomass which the authors suspect was due to insects emerging earlier in the year. This is because development is temperature-dependent for many insects, meaning warmer temperatures stimulate it to occur earlier than usual. This has already been seen in the wild in Germany, with a 2015 study finding the peak emergence of a freshwater insect community had moved 13.4 days earlier over a 42-year period. Taken together, these observations demonstrate that predicting how insects respond to different weather conditions is incredibly complex.
The importance of this study
The crux of this study lies in the author’s argument that changes in weather conditions over time cannot be unlinked from climate change. After all, climate change is effectively a deviation in weather conditions from usual. Therefore, this report could well show something sobering: climate change could have contributed to the insect declines seen in Germany and perhaps most temperate zones in recent years. However, on the brighter side, the study could also demonstrate the inverse: that climate change could increase insect abundance in the coming years. We have already seen examples of this in nature, with warm-adapted species such as the Broad Scarlet Dragonfly undergoing enormous range expansions in Europe. The truth is that we just don’t know yet how insects will fare amongst our changing climate, but it’s highly likely that some species might do worse than others. In light of this, the authors stress that continous monitoring of insects will be required in future years to understand their responses better and effectively target conservation policies towards the species in most danger.
The truth is that we just don’t know yet how insects will fare amongst our changing climate, but it’s highly likely that some species might do worse than others.
Naturally, the report also has its limitations. The authors are quick to acknowledge that insect biomass is not a proxy for insect diversity, citing studies that found insect biomass to be largely similar between seminatural and agricultural sites despite huge reductions in diversity in the latter. Consequently, true changes in insect diversity could paint a very different picture. Additionally, their analysis excludes numerous factors that could also explain declines, such as environmental pollutants. Although the dataset was collected in protected sites, run-off of agricultural pollutants is extremely common, and pesticides have even been found to linger in the atmosphere. As such, it is highly unlikely that the sites were truly unaffected by these other anthropogenic drivers of insect declines. However, this goes both ways—the authors also highlight how their results suggest an urgent need to control for weather conditions in other long-term studies of insect declines.
A call for action
Around the world, action has already begun to attempt to tackle the insect apocalypse we are facing. Numerous insecticides, such as the powerful nicotinic acetylcholine agonists neonicotinoids, have already been banned in the EU (although worryingly, the UK government recently approved their use under emergency authorisation for the third year in a row). Meanwhile, re-wilding and conservation programs are already working hard to protect and restore natural habitats where insects can thrive and reproduce away from manmade environmental stressors. On the other hand, climate change might be a slightly harder issue for us to tackle for insects, with recent reports suggesting that global warming will exceed the landmark 1.5-degree threshold well before 2027.
Nonetheless, the authors provide hope by describing a more local-scale approach to tackling these climate-induced declines. Many of our insects currently survive in small populations in fragmented patches of habitat, which are at greater risk of extinction from adverse weather events as the populations can afford to lose fewer individuals. By improving habitat quality and quantity at a small scale and boosting local population sizes, conservationists can effectively “buffer” the effects of adverse weather and reduce the likelihood of local extinctions. Luckily for us, hundreds of programs like these already exist—such as the American Prairie Project, which aims to create the largest continuous nature reserve in the United States (a remarkable 3.2 million acres). If Governments and local organisations prioritise these programs in their environmental policies in future years, insect populations might just be able to regain their buzz amidst our changing climate.
Preventing the ‘Insectinction’ will go far beyond protecting habitats and requires large-scale, global action.
Preventing the ‘Insectinction’, however, will go far beyond protecting habitats and requires large-scale, global action. But we can all start somewhere—perhaps by planting a wildflower meadow in our garden or by lobbying the UK government to join the EU in banning over 30 harmful pesticides post-Brexit. And of course, tackling climate change wouldn’t be a bad thing too.
