The Silent Extinction of Insects

Dr. Tomás Murray, Senior Ecologist with the National Biodiversity Data Centre explores our understanding of global insect losses

What’s happening globally?

Fundamentally, insects are “the little things that run the world”, (E.O. Wilson, 1987) and this is why the current conversation about insect declines is so necessary. Given that insects outrank all other animals in terms of species, numbers and biomass both worldwide and in Ireland, and that along with other invertebrates they are our pollinators, predators, decomposers, soil engineers and simply food for other animals, changes in their diversity and abundance can have profound consequences for how our landscapes function and human well-being.

Insects play fundamental roles in the ecosystems, so maintaining insect populations is essential. (From Gordon et al. 2019.)

Before the very real concerns about pollinator loss reached the level of public awareness it has today, for most people their perception of conservation involved the protection and restoration of large charismatic vertebrate populations and the spaces they live in. Consequently, a major success of the recent reports of alarming insect declines has been to trigger public attention to their plight and stimulate discussion on the value of insects. However, there have been some mixed messages about the decline and I think it’d be valuable to try and clarify what the science is (and is not) telling us and what I think is needed to capture the changes in Irish insects.

Firstly, the global picture: are we witnessing “insectageddon”, across the world? Insect declines have been documented across a whole variety groups, habitats and countries for decades, but at a fraction of the intensity of which vertebrate groups have been studied. For example, of the 69,903 species of vertebrate (mammals, birds, reptiles, amphibians and fishes), 48,101 (69%) have had their risk of extinction assessed via the International Union for the Conservation of Nature (IUCN) Red List process. In contrast, 8,121 out of 1,000,000 (0.8%) known insect species have been through the same process (latest table here).

The underrepresentation of invertebrates on assessments of species extinction risk (IUCN Red Lists). The area in red in each pie chart identifies how many species have been assessed as a percentage of the known species in each group. (From Eisenhauer et al. 2019.)

In addition, our knowledge of insects is very patchy in both time and space as it biased towards those countries that can afford to fund insect science. This became painfully obvious in the study published in April by two Australian-based researchers aiming to quantify global changes in insects by summarising the results of published academic papers documenting insects declines: 60 out of the 73 research papers included in their analyses were from either Europe and North America, and more papers were included from the UK than all of Africa, Asia, Australasia and South America combined (Sánchez-Bayo & Wyckhuys, 2019).

In fairness, this was the first ever global synthesis on insect declines and it was always going to be challenging given the data available to them. At minimum, their work highlighted how little we know about insects elsewhere on the planet. However, being selfish and just focussing on our part of the world, it does mean that the results of the synthesis are more relevant for us in northwest Europe.

Of the 73 insect studies included in Sánchez-Bayo and Wyckhuys (2019) analyses, 60 were from Europe and North America.

So, what did they find? With the above in mind (and some other methodological issues), the researchers found that 41% of the insect species included in their study were in decline and 31% have declined to the point they’re now under threat of extinction, broadly in line with the 45% decline found in a separate study conducted on invertebrates (in this case insects and nematodes) by Dirzo et al. in 2014. Given that we’ve described only about 1,000,000 species of insect and there’s an estimated 4.5 million more to be discovered, and that of the small fraction of those insects included in this global study potentially 41% are in decline, no wonder it grabbed headlines!

From Dirzo et al. 2014. A) trends in insects that have a had their extinction risk assessed (IUCN Red List); many more are decreasing than increasing. B) trends in UK populations of insects over the past 40 years. C) Long-term data from 452 species show global declines. The best data is from moths and butterflies (Lepidoptera) with strong evidence of 35% decline globally over 40 years. D) 7.6 times more species and 1.6 times more numbers of butterflies can be found on undisturbed sites vs. disturbed sites globally.

These percentage declines are all at the species level, but what about the quantity of insects flying, crawling, swimming and digging their way through our landscape? The second headline statistic from the paper was an estimate of the loss of insect biomass and the researchers estimated this to be 2.5% per annum. At face value this sounds modest but accumulatively means a 20% loss of all insects in 10 years, 52% loss over 50 years and a 92% loss over 100 years! But where did this 2.5% rate of decline come from? Well, from just three studies looking at long-term trends in total insect biomass in the England, Germany and Puerto Rico.

The first study from the UK looked at all the insects captured in four Rothamsted Insect Survey suction traps which have been hoovering up all insects 12.2 m above ground level for 30 years from 1973 to 2002, finding a 72% loss in flying insects in one out of four traps (Southall et al. 2009). The second study from Germany received quite a high profile and was probably the first to really stimulate the current interest in insect declines. Here the Krefeld entomological society maintained malaise traps across a network of 63 nature reserves over a 27 year period from 1989 to 2016, but only 26 sites were surveyed across multiple years, finding a 76% decline in flying insects (Hallmann et al. 2017). The third study from Luquillo Forest in Puerto Rico compared samples collected by sticky traps and sweep netting in 1976/1977 and repeated the methodology again 35 years later in 2011/2012, finding a 98% loss in canopy-dwelling insects and 78% for ground-foraging insects (Lister and Garcia, 2018).

Collectively, the losses estimated from these studies are shocking but each study has its flaws and limitations, as do all scientific studies, and in combination with the North American/European bias where most of studies were conducted, this means that it would be a stretch too far to say the science currently supports global insect declines: the jury is still out on insectageddon. Clearly absence of evidence is not evidence of absence and the enormous knowledge gaps in the status of insects outside of our part of the world is very much a product of miniscule resources available to entomologists across Africa, Asia, Australasia and South America.

What’s happening locally?

There have been two European-level Red list assessments of extinction threat in insects: one on bees and the other on butterflies. For bees, of the 1,965 species assessed 14% are in decline of which 9% are threatened with extinction but 56% of these species had too little information and are considered ‘data deficient’ i.e. we’ve no idea how they’re faring. Even in Europe with pollinators now having such a high profile in terms of conservation we still lack a lot of basic biological information on over half our bee species! In contrast, butterflies are a relatively intensely studied insect group and of the 435 species in the Red List assessment 19% are in decline, 9% are under threat of extinction and < 1% are data deficient.

As before, these assessments identify how many species are in trouble but not how the number of insects has changed in the European landscape. In Europe, we’re incredibly fortunate to have a long-term large-scale insect monitoring programme: the European Butterfly Monitoring Scheme. Based on the efforts of largely citizen scientists with some professionals mixed in, systematic counts of butterflies from 6200 locations across 16 countries (including Ireland!) are collated and analysed collectively to develop the EU Grassland Butterfly Indicator. Sadly, the latest version of this indicator shows there are now 39% less butterflies flying in our grasslands compared to 1990.

As butterflies are sensitive and immediate indicators of change, and broadly representative of other insect groups, this represents a dramatic loss of grassland wildlife beyond butterflies alone. Given the expansion and intensification of agriculture across Europe to the point where 76% of the landscape is now grazed, cropped or forested (EEA) it is highly likely that declines of this magnitude are happening outside of grasslands too. In Ireland, the same land-use statistic is very similar at 68% and if we look at the 934 insect species assessed in our Red Lists 26 (3%) are now extinct, 194 (21%) in decline of which 124 (13%) are under threat of extinction.

Similarly, our own monitoring schemes are now tracking changes in the number of bees and butterflies flying in the Irish landscape. Driven by our wonderful network of over 190 citizen scientists, 105 sites are being systematically monitored for bumblebees and 116 sites for butterflies. Based on eight species where we have enough data our populations of bumblebees have dropped by 17% since 2012: a marked decline over such a short period. In parallel, since 2008 we’ve lost 6% of our butterflies from the Irish landscape based on the 15 species with sufficient data. In both cases there is a lot of variation from year to year and, being insects, these trends can change rapidly over short time periods e.g. 2018 was a great year for butterflies with a jump of 23% in counts compared to previous year, but an appalling year for bumblebees with counts down by 24% on 2017.

Irish Butterfly Monitoring Scheme multi-species index of Irish butterfly populations 2008-2018 derived from 15 native species. The black dots and lines are the measured population sizes, the green line is the smoothed trend and the shaded area is the 95% confidence interval. Photo: Large Heath. Chris Martin, 2013.

Irish Bumblebee Monitoring Scheme multi-species index of Irish bumblebee populations 2012-2018 derived from eight species. The green line is the smoothed trend, the shaded area is the 95% confidence interval. Photo: Great Yellow Bumblebee. Nick Owens, 2012.

Given that the greatest declines insects presumably occurred in parallel with the modernisation of Irish agriculture in the 1960s and 70s, it’s frightening to think that we have no long-term data prior to 2008 and that current changes are only being detected by 23 species out of the 11,500 species! Despite this, we do compare well to our European neighbours as we are one of 16 countries systematically monitoring butterflies and one of two monitoring bumblebees. But what of the future and how can we avoid flawed decision making and landscape management by ensuring insects are a) there at all and b) being monitored?

What can we do now and in the future?

1. Get fully behind the All-Ireland Pollinator plan and give insects the space they need. The Pollinator Plan has excelled in promoting the plight of pollinating insects, improving public understanding of their value and most importantly empowering people to do something about it. Many of the recommended actions will benefit whole hosts of other insects too. Just like for all wildlife, we need to protect and expand existing areas that support large and diverse insect communities, restore ones we’ve damaged and link them all up so insects can move freely across the landscape. This approach is wonderfully encapsulated in ‘Bigger, Better, More and Joined’, by Sir John Lawton in his review of England’s wildlife and ecological network in 2010. Just like the Pollinator Plan, this concept of creating space of insects can be applied at garden, farm, landscape, county or national scales!

The Burren, a national biodiversity hotspot for insects as well as plants.

2. Get into insects. There’s no replacement for simply getting out and about and seeing what insects are around. Clearly, I think getting involved in one of our recording schemes (butterflies, bumblebees or dragonflies) is a great way of providing a focus for anyone new to insects, and by learning a particular group and they can then go on to help us monitor changes. Saying that, we’re a small team in the Data Centre and we can only provide support for the few major insect groups, but there’s a clear desire and immediate need for additional support for many other important insect groups too. Additional resources are needed to strengthen national capacity for insect taxonomy and to support the ever-dwindling pool of national experts to teach the next generation of Irish entomologists before sadly they and their knowledge are lost to us.

3. Expand long-term insect monitoring programmes. Of course I’m biased but I feel strongly that citizen science is a key tool to both improving the public understanding of the value of insects and a genuine research approach to tracking changes in insects. Ireland is very much set-up for insect citizen science in that we have a ‘rich enough’ insect fauna to be useful for rigorous monitoring: not too few species to be insensitive to change; not too many to be unfeasible to teach to non-specialists. We have a diverse range of insect groups that can be broken down into 20-50 species that can be mastered by anyone willing to do so. However, there will always be some groups that only professionals, in combination with genetic techniques, could be feasibly monitored over long-periods of time.

Although it is now widely accepted that insects provide critical ecosystem services and they are still insufficiently represented in national wildlife monitoring programmes. For long-term monitoring we need to identify a core network of sites on state-owned land with targeted insect monitoring of multiple key indicator groups. This could even be expanded to measuring the ecosystem services of these insect groups too e.g. decomposition of leaves and wood, pollination and flower visitation, predation of baits.

Imagine a future world where the lines between professional and citizen scientist are blurred: at core sites ecologists could do the most labour-intensive and technically challenging work, whilst also working in collaboration with citizen scientists conducting parallel insect and ecosystem service monitoring at a broader network of sites. This future world may also include automated monitoring, such as acoustic monitoring or a network of insect camera traps like those currently being trialled in the Netherlands.

Prototype insect camera trap being trialled this year in the Netherlands. Credit: Radboud University.

4. Fully mobilise, centralise and make freely available all the insect data for Ireland. There are still large quantities of insect information contained in our museums, universities and environmental consultancies that would be invaluable in the development of national checklists and baseline maps against which we can make comparisons of change. As with building taxonomic capacity for insects nationally, museums can play a key role in raising the profile of insects to the general public through their exhibitions, managing reference collections to teach future entomologists and the collation of historical insect data.

In parallel, researchers at universities and professional ecologists will be at the forefront of collecting high quality contemporary data on insects and require not only the default ‘more funding’ but also right digital infrastructure to allow them to centralise their insect data easily. Fundamentally, to best inform insect conservation in Ireland we need the best insect data, so having big, open and linked national databases will go a long way to helping us achieve this. If we want to have any hope of being able to predict how our species and habitats are going to change, and then identify the best strategies to both mitigate and adapt to these changes, failing to include insects in this process will result in appalling predictive models and consequently very poor decisions will be made.

Dr. Tomás Murray is the Co-ordinator of the Irish Bumblebee and Butterfly Monitoring Schemes and Senior Ecologist with the National Biodiversity Data Centre

What’s happening globally?

What’s happening locally?

What can we do now and in the future?

Further reading: