The last few years has seen a multiplicity of reports on the “worrying” and even “catastrophic” decline of insect population levels. Such claims must be thoroughly verified, partly because alarmism can lead to apathy. A recent report reviews the situation in a holistic fashion, and the picture is more complex than intially reported.
One of the biggest questions today is whether we are witnessing (or causing) the 6th mass extinction. We know that previous mass extinctions did not happen in a decade or two, but rather over millions of years. There are billions of species on the planet, and for 70% or more to disappear, it takes some profound changes that occur over what seems like a long time for humans. Long enough a time that it could creep up on us unnoticed.
The latest Living Planet Report (WWF, 2020), the most comprehensive assessment of our wildlife’s wellbeing, has reported a 68% average decline in the population sizes of all monitored species since 1970. Of highest alarm are the amphibians, of which half the species are imperiled, and coral reefs which could all but disappear by mid-century.
A number of reports have also called attention to declines in insect numbers and variety, although it is harder to determine whether the rates are above or below those observed in larger species. Extreme declines were described in western Europe and California’s Central Valley, where humans are highly concentrated, but there is little information from the tropics, where far more insect species exist.
Entomologists from around the world gathered for a symposium in November 2019, aiming to gather the latest information in one place. They identified data gaps and inconsistencies, and ultimately attempted to determine the state of the insect world.
How are insects doing?
Reports from the past decade have described many cases of catastrophic loss, yet conflicting studies demonstrate vibrant proliferation and expansion. A 2018 article published in the New York Times called “The Insect Apocalypse is Here” received no less than six rebuttals and many blog posts denouncing the conclusions.
The issue is simply how difficult it is to assess insect population trends.
Nevertheless, two major metaanalyses concerning insects were published in 2020, gathering data from up to 166 reports spanning up to 91 years of observations. One found an overall decline in terrestrial insect abundance of 1% per year. The other said there was an increase in freshwater species diversity, though not abundance, while European terrestrial species showed stronger signals of decline. The results are still under review, but the conclusion is this: the greatest threat of the Anthropocene is the incremental loss of populations due to human activities. Such losses often go uncounted in studies, and this is why it is so elusive.
What is the Cause of Insect Decline?
From the evidence it seems that insects are suffering a slow death by a thousand cuts”. Depending on the location and species, causes of decline can include land-use change (deforestation in particular), climate change, agriculture, newly introduced species, nitrification (fertilizer use), pollution, insecticides, herbicides, urbanization and light pollution. They often experience multiple stressors simultaneously, and it is therefore difficult to identify the main culprit.
A good example is that of the US domesticated honey bee. Investigations into its decline have pointed to introduced mites, viral infections, microsporidian parasites, habitat loss, artificial foods used to maintain hives and inbreeding. Over 14 years later, we still do not know which was most damaging.
Where From Now?
First, issues with population trend assessment need to be addressed. This means collecting more data from places that aren’t the US or Europe, and standardizing monitoring techniques.
Encouragingly, funding to support insect conservation is on the rise, and there is a rise of non-academic interest in the topic. iNaturalist is an online resource for taxonomical identification with over 13,6 million entries added since 2010.
Regardless of the paucity of information, it is clear that we are driving a significant decline in biodiversity which affects all living things and the remedy is to fight for a more environmentally aware and sustainable future. The main thing for us to do as individuals is elect the right officials who will apply pressure to the large organizations which cause most of the damage.
In conclusion, the insect apocalypse is not yet here, and we thankfully still have time to turn things around. However, the next will be a key decade in determining how bad things get this century.
This article was written by Owen Mulhern. Cover photo by nutmeg66, on butterfly-conservation.org.
“Insect decline in the Anthropocene: Death by a thousand cuts”. David L. Wagner, Eliza M. Grames, Matthew L. Forister, May R. Berenbaum, David Stopak. Proceedings of the National Academy of Sciences Jan 2021, 118 (2) e2023989118; DOI: 10.1073/pnas.2023989118