Newly published research from Germany reveals that three quarters of all flying insects have vanished since 1989.
That the Earth is currently in the throes a mass extinction event is no secret. The scale of biodiversity decline in the UK was comprehensively described in last year’s State of Nature 2016 report, which revealed that 56% of the UK species studied have declined since 1970, while more than one in ten (1,199 species) of the nearly 8000 species assessed are under threat of becoming extinct in the UK.
Sadly, this week saw further evidence for widespread biodiversity decline come to light, as a study monitoring the abundance of flying insects in nature reserves across Germany was published in the journal PLOS One (Hallmann et al. 2017). In the paper, the team of Dutch and British scientists report that flying insects have declined by three quarters in just 27 years.
The research is based on the impressive efforts of amateur entomologists from the Krefeld Entomological Society, who have been sampling flying insects in nature reserves across Germany for the past three decades. Since 1989, these dedicated volunteers have used malaise traps, tent-like structures that allow insects to be sampled in a standardised way, to capture 1503 samples of flying insects over 16908 trapping days. The 63 nature reserves sampled as part of this research are composed of a wide range of semi-natural habitats including meadows, dunes and heathland.
While the research team have not yet made much progress identifying and counting the vast number of insects captured as part of this impressive monitoring project, they have now analysed the biomass data, and the trend for biomass caught per day is deeply troubling. In the early years of the study, the malaise traps were catching approximately 9g of insects per day. By 2014, the average catch had plummeted to about 1g per day, with the highest catch at any one site just 2g per day. The data show that the annual average biomass of flying insects in German nature reserves has fallen by 76% in just 27 years, with the most severe declines (82%) occurring in mid-summer, when flying insects are typically most abundant. “The fact that the number of flying insects is decreasing at such a high rate in such a large area is an alarming discovery,” said Hans de Kroon, an ecologist based at Radboud University in the Netherlands, and one of the study’s authors.
This decline is enormous, not only in scale but also in terms of its implications for Europe’s ecological systems. Professor Dave Goulson of Sussex University in the UK, who was involved with analysing the data, commented “Insects make up about two-thirds of all life on Earth [but] there has been some kind of horrific decline. We appear to be making vast tracts of land inhospitable to most forms of life, and are currently on course for ecological Armageddon. If we lose the insects then everything is going to collapse.”
Up until now the evidence for declining insect abundance was limited to relatively well-monitored groups such as butterflies, moths and bees. This study suggests that the problem is affecting a far greater range of insect groups, and the fact that the declines were observed in nature reserves provides a strong indication that our current approach to conserving biodiversity within protected areas is not effective for many species. “The fact that the samples were taken in protected areas makes the findings even more worrying” said lead author Caspar Hallmann, who is also based at Radboud University. “All these areas are protected and most of them are well-managed nature reserves. Yet, this dramatic decline has occurred.”
In addition to sampling insects, changes to plant species within the reserves, as well as changes at the landscape scale outside of the reserves, were recorded as part of the study, as were detailed weather measurements. The habitats making up the nature reserves appear to have changed little over the last 30 years, and while the majority of land surrounding the nature reserves is agricultural, this is also thought to have experienced little change since the study began in 1989. Variation in the weather accounts for some of the observed fluctuations within seasons and between years, but does not explain the enormous decline in insect abundance.
It is clear that something catastrophic is taking place in Germany, but at present it is not at all clear what that something is. One possibility is that the observed decline is a consequence of historical land use change, which drove massive habitat loss and fragmentation earlier in the 20th century. These changes may have compromised the long-term viability of populations of flying insects, with the declines observed over the last few decades constituting the gradual reduction in abundance over time as populations slowly disappear from the landscape. A second possibility is that the relatively recent introduction of systemic insecticides, such as neonicotinoids, are contributing to the observed declines. There has been much research into the impact of neonicotinoids recently, and the evidence strongly indicates that use of these highly toxic chemicals could pose serious problems for invertebrates that are exposed to them. One of the major problems with neonicotinoids is that they appear to persist in the environment for a very long time, contaminating soils, streams, flowering plants and hedgerows in agricultural landscapes in the longer-term. To date scientific research has linked the use of neonicotinoids to the decline of butterflies, bees, aquatic invertebrates and insectivorous birds. It is possible that these agricultural chemicals might be contaminating the nature reserves themselves. Another possibility is that flying insects might be exposed to the chemicals when they leave nature reserves. We know that many flying insects use resources at the landscape scale, and the study authors speculate that neighbouring fields dowsed in pesticides may become inhospitable places from which insects never return. Therefore, ongoing human activities in the surrounding landscape could mean that populations of many flying insects are currently doomed, no matter how well nature reserves are managed.
Flying insects have extremely important ecological functions for which their abundance is crucial. They are integral to natural ecological systems, playing key functional roles as pollinators of wild plants and agricultural crops, and predators and prey in food webs. Thus, a decline in abundance on the scale detected in this study will have disastrous consequences for the integrity and resilience of ecological systems. In addition, the degradation of ecosystem services has serious implications for human society. As the American biologist E.O. Wilson once said “if all mankind were to disappear, the world would regenerate back to the rich state of equilibrium that existed ten thousand years ago. If insects were to vanish, the environment would collapse in to chaos”.
We do not currently know whether the dramatic decline in flying insects detected in this study has also occurred elsewhere, but, given that land use in Germany is broadly very similar to that in other European countries, we can reasonably expect this to be the case. This rather pessimistic view is unfortunately supported by monitoring data collected for the better-studied groups of flying insects, such as butterflies and bees, as well as population trends in insect eating birds. Birds that specialise in feeding on flying insects, such as swallows, swifts and the spotted flycatcher, are declining at an alarming rate across Europe and North America, suggesting that the decline detected in Germany may be a widespread phenomenon. While we are probably right to suspect this, the team of scientists involved in the study emphasise the urgent need for further work to corroborate their findings in other regions, and to investigate the factors causing the observed declines in more detail.
When the State of Nature 2016 Report was launched last year, Sir David Attenborough commented “The natural world is in serious trouble and it needs our help as never before”. This study provides further evidence of the catastrophic impact that human activity is having on our wildlife. Studies such as this one are extremely valuable for understanding what is happening to our natural environment and for shedding light on the most likely drivers of biodiversity decline, but it is also vitally important the we focus on developing effective solutions. Monitoring declining insect abundance without taking appropriate action is like having a seriously ill patient in hospital hooked up to various machines monitoring declining health, without administering any effective treatment.
In addition to developing effective interventions, it is also vitally important that we remain optimistic about our ability to affect positive change in the face of such a depressing outlook. We would do well to remember that Martin Luther King Jr. famously said, “I have a dream,” not “I have a problem.” The trouble with focusing too much on the problem is the danger that it could lead to hopelessness, which might further contribute to the decline of the natural world through inaction. In this case, failure to take action to address the factors driving declines in flying insects will mean that there will be precious little insect life remaining in the not so distant future.
It is clear that governments, businesses, conservation organisations and individuals will all need to do their bit if we are to address the environmental issues highlighted by this study. As rightly pointed out by Hans de Kroon, a good start would be “to do less of the things that we know have a negative impact, such as the use of pesticides and the disappearance of farmland borders full of flowers”. In addition to implementing changes to our agricultural systems, we also need to think about how we can enhance other land use types to deliver significant biodiversity benefits. Like agricultural land, gardens account for a significant proportion of land cover outside of nature reserves in Europe. All of us who are fortunate enough to care for some outside space can contribute to the solution by providing insects with the resources that they need. Improving habitat by providing a diverse range of flowering plants rich pollen and nectar, suitable nesting sites, and other essential resources, will help to support flying insects as they move through the landscape. Conservation success often depends on the accumulation of small-scale actions, and we can all make a significant contribution no matter how small our patch of land is.
While the outlook for the natural world is bleak at present, as the saying goes “it is far better to light a candle than to curse the darkness.”