Insect Armageddon

It has become increasingly clear that in Britain and around the world, insect populations are suffering catastrophic decline

How did the problem come to light?

In recent years, many people have noticed what is known as “the windscreen phenomenon”. In the past, a car journey in high summer would have left the windscreen plastered with squashed flies, gnats, mosquitoes and moths. Today, even after long journeys, windscreens are largely clean. Similarly, as the environmental journalist Michael Mccarthy noted in his book The Moth Snowstorm, the blizzard-like clouds of moths that filled car headlights on summer nights in the 1950s and 1960s are now hardly ever seen. Over the past decade, entomologists have concluded that these are symptoms of a crisis in the natural world. Across Britain and Europe – indeed, across much of the world – insect numbers are in sharp decline.

How bad is the situation?

Compared to mammals, birds and fish, insects aren’t well studied, largely because we don’t much like them – except for butterflies, moths and bees. And in their case, the statistics are grim. Bee numbers in Europe and the US have declined by 30% to 40% in recent decades. European butterfly populations have halved since 1990. In 2013, a 40-year study showed that two-thirds of the UK’S 337 common larger moth species had declined substantially. The V-moth, once widespread, had decreased by 99% since 1968. It is hard, though, to get a sense of the overall picture: there are a very large number of insects, and insect species (about 25,000 in the UK alone). Of all known animal species, mammals make up less than 0.5%; insects make up some 70%. Recently, though, a series of studies have thrown light on the broader situation.

And what do those studies reveal?

A major survey by the Zoological Society of London in 2012 concluded that many insect populations were in severe decline. A 2014 study in the journal Science, combining data from detailed research conducted across the world, indicated a 45% overall drop in insect abundance. But the most alarming findings came last year, when entomologists in Germany published the results of a long-term study. Over a period of decades, they had set up special tents that act as traps for flying insects in 63 different nature reserves across the state of North Rhine-westphalia. And they found that the average weight of insects trapped fell by 76% between 1989 and 2016. In summer, when insects are most numerous, the decrease was 82%. The study shows that “there has been some kind of horrific decline”, warned Professor Dave Goulson of the University of Sussex “We appear to be making vast tracts of land inhospitable to most forms of life, and are currently on course for ecological Armageddon.”

Why is this happening?

The causes are not fully understood, and there is no single explanation. Insects are endangered in a large number of ways, notably by climate change, urbanisation and loss of habitat (especially in the developing

world, where deforestation threatens millions of species). Light pollution messes with their navigation systems and disrupts their mating, while cars don’t help: one study estimated that hundreds of billions of insects in North America were being killed by vehicles every year. But the German study ruled out some of the most obvious causes, such as changing weather conditions and habitat loss (the nature reserves were managed, and changed little over the decades).

So what was the likely cause?

It seems probable that they were affected by changing conditions in the farmland surrounding the reserves – driven by the long-term intensification of farming. Flower-rich habitats such as hay meadows, field borders and hedges have been lost. The use of fertilisers, herbicides and pesticides has increased. Intensively farmed wheat and cornfields support virtually no insect life. And the ubiquitous use of pesticides seems to be particularly damaging. Neonicotinoids – some of the world’s most used pesticides – are a prime suspect: they have been linked to bee colony collapse disorder, and have been found in high concentrations in nectar and pollen near treated fields. Neonicotinoid poisoning has been shown to affect insects’ ability to navigate and communicate.

Why does the loss of insects matter?

About a third of the world’s crops – mostly in orchards and fruit fields – rely on bees, flies, and other insects for pollination. More generally, insects play a crucial role in most ecosystems (see box). Wild flowering plants rely on them for pollination. They provide food for birds, mammals, fish, reptiles and amphibians. Insect decline is the best explanation for the loss of more than half of Britain’s farmland birds since the 1970s: a recent study showed that the plunge in cuckoo numbers is linked to declines in the tiger moth caterpillars on which they feed. Insects also play a vital role in decomposing organic matter, which makes soil fertile. And balanced insect populations ensure pests are kept under control: ladybirds and lacewing larvae prey on aphids, for instance.

So what can be done?

Setting up more buffer zones of wildflowers and native plants around single-crop fields is one solution backed by environmentalists. Herbicide and pesticide use must also be reduced: another study, into the catastrophic decline of the grey partridge, showed that lowering herbicide levels raises the number of insects – and that this, in turn, raises the number of grey partridges, which feed on sawflies and other insects. Some important steps have already been taken. An Eu-wide ban on neonicotinoids is expected by the end of 2018. In England, farmland and woodland butterflies have slightly recovered since 2012. In June, the EU proposed its first initiative to address the decline of wild insects. Time will tell whether these are enough to reverse the vast loss of insect life that is occurring.