That evening on the terrace, in the yellow glow of the outside light, it took a lull in the dinner conversation for anyone to notice that something was missing. Where were the dull thwacks of flying insects bumping against the lightbulb? Even the tuneless orchestra of cicadas or crickets, whichever they were (no one was quite sure), had stilled its instruments.

“Where have all the insects gone?” someone said. We looked down at the ground, littered with spilled crumbs from our plates. The usual marching army of ants had failed to appear. This was in Sicily this summer, during a weeks-long stretch of oppressive heat. The weather app said it was 36C but noted that it felt like 42C. Perhaps it was too hot even for bugs, someone quipped. Or perhaps it was the surrounding farms, all those tomato growers. Maybe they’d been spraying pesticides. We shrugged and continued to eat. But back in a much cooler UK, their absence was a feature of my garden too. The buddleia, usually a magnet for bees and butterflies, was silent. One day, a lone bumble bee hovered over the trailing pink petunia of the hanging basket. It took a week before I noticed another one. Was it just me? Was it just my garden? No. No. #insectarmageddon and #insectapocalypse were trending on social media. Buglife, a UK conservation charity, was warning that something had “gone radically wrong” for insects. Even the former Top Gear presenter Jeremy Clarkson, no friend of climate activists, had posted that he was “alarmed” by the lack of butterflies.

Turns out ecologists and entomologists around the world have been warning about declining insect numbers for years. The culprits are climate change, habitat loss, light pollution, intensive farming, pesticide and fertiliser use. But it’s a struggle to get people to act. After all, we humans have a complicated relationship with our six-legged fellow Earth dwellers. Who can forget the horror of Kafka’s Metamorphosis, where a travelling salesman wakes up one morning to find himself transformed into a bug, or the morality tales of the Victorian age that saw naughty children turned into insects? Up close, even the face of a butterfly or bee is disturbingly alien. Maybe we’ve been “othering” insects to oblivion. 

Yet our own existence depends on a thriving insect world. Studies show that where more insect species are present, pollination is more reliable and resilient. As Dave Goulson, professor of biology at the University of Sussex, points out in his book Silent Earth: Averting the Insect Apocalypse, about three-quarters of all crop types grown by humans require pollination by animals, the vast majority by insects. “We could not feed the global human population without pollinators,” he writes.

It’s not just about bees and butterflies, the poster children of the pollinator world. Other, less photogenic pollinators such as hoverflies, moths, wasps, soldier beetles and earwigs are also showing declines. Several of these species don’t just pollinate. They also eat the pest insects that ruin crops.

A UK parliamentary report in March this year noted that, internationally, the economic value of pollinators has been estimated to be worth over £134bn to agricultural markets. Already, in the apple and pear orchards of south-west China, depleted populations of pollinators have forced farmers to hand-pollinate their trees, carrying pots of pollen and paintbrushes with which to individually pollinate every flower. If it sounds labour-intensive and time-consuming, that’s because it is.

But try convincing, for example, beachgoers on Misquamicut State Beach in Rhode Island that insect numbers are plummeting. In July this year, they were swarmed by hundreds of thousands of dragonflies. The problem is that data on insects is patchy and varies not just by geographical region and time of year but also by species. Interpreting it is fiendishly difficult. There is no unified global monitoring system for insects. Their sheer number makes it impossible; insects account for the majority of species on the planet. We’ve named about one million of them but there are millions more we don’t know about and whose role in balancing ecosystems remains a mystery. Which brings us to the point of a fly, or a dung beetle for that matter. Without them we might be swimming in excrement and wondering what to do about rotting animal carcasses.

“Probably, we’ve lost insect]species that have not yet been named,” Goulson says.

Perhaps alone among the sciences, entomology relies heavily on volunteers and “citizen scientists” for data collection. People like Roger Morris in the UK, who loathes the term citizen scientist, preferring ‘‘community scientist” instead. Morris is a retired ecologist and estuarine geomorphologist, but his passion is the hoverfly, an insect often mistaken for a wasp or bee. It’s one of nature’s most important pollinators and some species of hoverfly are now endangered in the UK and Europe. Since 1991, Morris has volunteered as joint organiser of Britain’s Hoverfly Recording Scheme and co-authored a book on the species.

Every day, he goes out armed with a sweeping net and a hand lens. “There’s a lot of watching, just literally walking and watching, and looking very weird,” he says. “Very often you’ll see me with my head stuck in the net because I’m busy trying to catch something with my hand.” Back home, he sticks his pickings under the microscope for identification, meticulously recording his findings in a spreadsheet, data he shares with research centres and universities. He recalls a sunny morning in June last year when he “returned home almost in tears” with only a meagre haul.

Morris is a rare breed. Often volunteer data collection relies on the welcome enthusiasm of a less expert general public; initiatives such as Bugs Matter, run by the Kent Wildlife Trust in partnership with Buglife and the Royal Society for the Protection of Birds, where participants count the number of insect splats on their car’s number plate at the end of a journey and submit the count via a mobile app, along with a photograph. The last Bugs Matter report showed the abundance of flying insects sampled on vehicle number plates fell by 78 per cent in the UK between 2004 and 2023.

Some of us might remember this “windshield phenomenon” from our youth; how, during long drives in the summer, our parents would stop and scrape dead invertebrates from the car windscreen. Others might remember a time when it was normal to see a blizzard of moths dance in the headlights. “If you drive along any country lane now, it’s a rare thing to see a moth,” Morris says. 

Ecologists call this the “shifting baseline syndrome”. “Each new generation views the world they grew up in as the reference, rather than recognising that biodiversity is already depleted,” the UK’s 2023 State of Nature report notes. No one thought to record insect numbers when they were obviously plentiful. Even today, many insect species continue not to be monitored at all. 

So, beyond a niggling sense that there are fewer of them about, where is the definitive evidence that insects overall are in decline? Whenever a big report has come out, there has been blowback. In 2017, a German study found that the volume of insects — rather clinically referred to as “biomass” — had dropped more than 75 per cent over a period of 27 years from 1989 to 2016. That prompted headlines around the world of an “insect apocalypse”.

But critics were sceptical: the fall could be explained away by a disproportionate loss of just a few heavy insect species. The survey had succumbed to bias, they argued; scientists had sampled areas where there had been large numbers of insects to start with, and don’t larger-than-average insect populations fluctuate more than smaller ones anyway? 

In 2019, those data biases were addressed in another study. Hundreds of German forests and grasslands were surveyed over 10 years, from 2008 to 2017. Its conclusion was equally alarming. The biomass of arthropods, a classification that includes insects, spiders and any animal with an outer skeletal cover, was down by over two-thirds. The number of species had dropped by a third. 

A global study followed in 2020, a meta-analysis encompassing long-term data sets of insect populations, including those that had found increases. It concluded that terrestrial insects were declining at a rate of 9 per cent per decade but noted increases in freshwater insects. That clashed with an earlier meta-analysis that warned of the “extinction of 40 per cent of the world’s insect species over the next few decades”. Cue more headlines about “insectaggedon” and the collapse of nature.

You get the picture: scientists agree there’s trouble in the insect world. They just can’t agree exactly how much trouble. Uncertainty is a difficult message to convey to the public. There is a “great parallel with climate change”, said Simon Potts, professor of biodiversity at the University of Reading, in his evidence to MPs for March’s parliamentary report on UK insect declines, published this year. “One of the risks is that it . . . can place the question in the public’s mind, ‘If the scientists cannot quite agree on this, who do we believe?’” 

Huge knowledge gaps don’t help. In the tropics, where most insects live, only sparse monitoring is taking place. A tradition of amateur entomology seems to be peculiar to northern Europe and North America, possibly something left over from the Victorian era, a time when chasing after insects with nets and collecting them as a hobby went from being a “futile and childish” interest, according to John Clark in his book, Bugs and the Victorians, to a legitimate academic pursuit. 

Which may explain why one of the world’s largest and longest-running insect recording projects is the UK’s Butterfly Monitoring Scheme. It has been going since 1976. Volunteers walk along a fixed route every week or so in the spring and summer, counting butterflies within a set distance either side of their path. That standard methodology is great for people such as Gary Powney, a quantitative ecologist at the UK Centre for Ecology & Hydrology, whose job is to crunch through insect data. The BMS’s standardised counting system “means those issues around trying to deal with biases in the data are slightly reduced”, he says. 

The UKCEH and other research institutions are now working on the Druid (Drivers & Repercussions of UK Insect Declines) study. It aims to provide a definitive answer on whether UK insects are declining overall. In fact, the UK is one of the best monitored countries globally for insects, thanks not just to the Butterfly Monitoring Scheme but also to the establishment of the Rothamsted Insect Survey. 

It’s the hottest day of the year and at Rothamsted in rural Hertfordshire a beetle scuttles across the warm ground to shelter in the shade of the path’s grass edging.

 A delighted Kelly Jowett, an applied entomologist, crouches down. “That’s a Pterostichus madidus,” she says, without skipping a beat.

“Don’t step on it,” cautions her colleague Dion Garrett, a molecular entomologist. “It’s a good guy.”

There’s a lot of identifying “good guys” and “bad” ones at Rothamsted, an agricultural research centre that’s been running two national insect trap networks since 1964. In the centre’s fields stand two 12-metre suction towers — Garrett describes them as “upside-down vacuum cleaners” — positioned to suck in aphids, tiny insects that are among the major global pest groups. Every day, every single trapped aphid is put under the microscope for identification. As Jowett says, “It does take a certain, very niche person to look at insects.”

There are a couple of light traps at Rothamsted too, part of a national network run entirely by volunteers. Most of the 1,500 species it has trapped over time are in the moth family. But while aphid populations appear more or less stable, populations of larger moths have shown a worrying 33 per cent decline in Britain over the past 50 years, according to a report compiled with data from Rothamsted Research, the wildlife charity Butterfly Conservation and the UKCEH. Even more perplexing is another Rothamsted study, which showed that moth declines were higher in woodlands than on farms and in cities, in areas the authors described as “relatively shielded from the effects of chemical and light pollution”. They speculated climate change played a role. 

Goulson notes that woodland butterflies show the same pattern. “Climate change and a huge number of deer overgrazing the understorey probably don’t help,” he says. “The extent of woodland may have increased, but their quality for wildlife has probably declined.”

Roger Morris, the hoverfly specialist, describes insects as “climate change canaries . . . You’ve got to remember what an insect is,” he says, pointing out that by the time we see them flying around as butterflies and bees, they’re in their reproductive state. For the rest of the year, they’re in breeding season and exist as larvae, eggs or pupae. “So if you get a period of drought and you are, say, a fly larva that relies on a wet place and that wet place turns into a sheet of concrete, you are dead,” he says. One drought may reduce numbers but, he adds, “if that then happens time and again, it’s death by a thousand cuts.”

That may go some way to explaining nature’s silence during our Sicilian dinner this summer. It doesn’t, however, explain the current dearth of insects in my garden. After all, there was higher-than-average rainfall in the UK this spring. But Jowett at Rothamsted reckons heavy spring rain may have affected caterpillars’ food supply. “The host plants that [they’re] feeding on weren’t doing as well,” she says. “And as a result of [food plants] being more sparse, the populations of butterflies are a bit more sparse.” 

The question is how many boom-and-bust cycles can insect populations endure before this wipes many of them out? Entomologists note that, given the right conditions, populations can bounce back. Some steps may be as simple as turning off artificial light. A recent study in China found that trees in Beijing, lit by street lights at night, seem to have tougher leaves and less damage from insects. In other words, insects are probably being starved out of the area. Policies that support farmers to treat the use of chemical pesticides as a last resort is another obvious answer, if not banning some of them outright. Greening our cities may help. Not mowing our lawns. Leaving sections of farm fields to grow wild, an insect’s natural habitat. But also, acting on climate change and encouraging careers in entomology because, as any entomologist will tell you, there are a lot of insect species and not enough entomologists. 

That means addressing our attitudes to insects, particularly in the west. Those annoying fruit flies hovering around your food bin? They’re simply doing what they were born for. They’re recycling. Besides, they’re food for birds, and UK bird populations have crashed in recent years. Nature is a finely tuned symphony. It doesn’t take much to send it out of key.

For some insect species, though, it is already too late. Possibly only the most passionate entomologist shed tears when the St Helena giant earwig was officially declared extinct in 2014. These days, one of the few places that houses a specimen is London’s Natural History Museum. Who knows what, if anything, went through its mind as it was preserved for posterity. The Victorian British entomologist Margaret Fountaine gave us a sense when she wrote about her butterfly collection, ruefully describing herself as the insect’s “tormentor”.

“She stretched out her long proboscis, and seemed to be feeling about to find something to suck,” Fountaine writes. “And I? I gave her petrol, till she died! And that was all!”