How climate change is affecting the insect world at a rapid pace|

TThe climate crisis is poised to dramatically alter the world around us. The calamity will affect many species, not just humans. As coral reefs become ghostly white and the tropical rainforests fall, huge die-offs across the animal kingdom will occur. Some researchers speculated that insects might be less susceptible to climate change than birds, mammals, and other groups of animals for a time. With their large, flexible populations and resistance to mass extinction events in the past, insects are sure to do better in the face of climate crisis.

Unfortunately, no. Scientists still fear that the world will warm to 3.2C by the end this century. Cop26 promises that the temperature will drop to 2.4C. Half of all insect species could see their habitats shrink to half the current level. This is more than twice the number of vertebrates. It is also higher than for plants because they lack wings and legs that can quickly move around. This is in addition to the current problems faced by insects due to habitat loss and pesticide usage. “The insects that are still hanging in there are going to get hit by climate change as well,” says Rachel Warren, a biologist at the University of East Anglia, who in 2018 published research into what combinations of temperature, rainfall and other climatic conditions each species can tolerate.

Some insects, like the dragonflies, can withstand the creeping change with ease. Most insects are not. Moths and butterflies are also mobile. However, at different stages of their lives, they rely on specific terrestrial conditions and certain plant foods. Many are still vulnerable. The fact that pollinators like bees or flies are unable to travel long distances makes it difficult for farmers to grow certain foods. This is not only because of a lack in pollination, but also because large areas of land become unsuitable for growing many crops beyond 3C. As tropical regions experience unprecedented temperatures, the area available to grow coffee and chocolate will shrink.

The climate crisis interlocks with so many other maladies – poverty, racism, social unrest, inequality, the crushing of wildlife – that it can be easy to overlook how it has viciously ensnared insects. This problem is also more difficult. “Climate change is tricky because it’s hard to combat,” says Matt Forister, a professor of biology at the University of Nevada. “Pesticides are relatively straightforward by comparison but climate change can alter the water table, affect the predators, affect the plants. It’s multifaceted.”

From the poles to tropics, insects are under attack. The Arctic bumblebee Bombus polarisIt is found in Alaska, Canada and Scandinavia, as well as Russia’s northern extremities. It is able to survive near-freezing temperatures due to dense hair that traps heat and its ability to use conical flowers, like the Arctic poppy, to magnify the sun’s rays to warm itself up. The Arctic is experiencing record temperatures, which could lead to the bee’s extinction by 2050. As their environment changes, alpine butterflies that depend on only one or two high-altitude plants are also in danger.

Research in the UK has shown that glowworm populations have plummeted by three quarters since 2001. The primary cause is the climate crisis. The larvae of the insects feed off snails that can thrive in damp conditions. However, a string of hot and dry years has left the glowworms severely short of prey.

These sort of losses in Europe have challenged previous assumptions that insects in temperate climates would be able to cope with a few degrees of extra heat, unlike the mass of species crowded at the world’s tropics that are already at the upper limits of their temperature tolerance. Researchers from Sweden and Spain found that most insects living in temperate areas are inactive during cold seasons. When just the warmer, active, months of insects’ lives were considered by the scientists, they found that species in temperate areas are also starting to bump into the ceiling of livable temperature. As Frank Johansson, an academic at Sweden’s Uppsala University, glumly puts it: “Insects in temperate zones might be as threatened by climate change as those in the tropics.”

BThe pointy end of rising heat is at the snare of umblebees, large furry insects that are permanently sewn into their winter jackets. A Study at the University of Ottawa in 2020The study found that North American bumblebee populations have almost halved while European numbers are down by 17%.

Although some scientists caution that this research does not prove causation of the correlation, there is broad acceptance that changes to temperature and rainfall could overwhelm insects already under threat. Scientists revealed the good news in 2019, for instance. Neun new species of beesIt was discovered that the Fijian island in the South Pacific had a large number of these species. But, scientists soon found out that many of them could be at risk of extinction from climate change due to their changing mountaintop habitats. “In the future, climate change is going to be the nail in the coffin for quite a lot of creatures which are already in much reduced numbers,” says Dave Goulson, a University of Sussex ecologist. “They’ll simply be unable to cope with a 2C rise in temperature and all the extreme weather events that are likely to go with that.”

Even the Amazon rainforest is seeing its complex relationships shattered. The increasing incidence of the El Niño phenomenon, coupled with human interventions such as deforestation, are spurring more intense drought and wildfires. Researchers were shocked when they discovered that the El Nino phenomenon was causing a population collapse in the humble dungbeetles. These beetles are key distributors and indicators species of ecosystem health. Counts of beetles before and after an El Niño event in 2016 found that insect numbers had been cut by more than half within the studied forests. The climate crisis is making Amazon drier, brittler, and more likely to catch fires. Additionally, it is removing the dung beetles, which help to regenerate burned forests. “I thought the beetles would be more resilient to drought than they were,” says Filipe França, the Brazilian scientist who led the research. “If climate change continues we’ll not only see less biodiverse forests but also make them less able to recover after further disturbances.”

Insects feel every jolt to regular life rhythms because they are so intertwined with the environment. The established life cycle of insects is being disrupted by spring being pushed earlier in the year. The UK sees moths, butterflies, and other insects emerge from their cocoons six days earlier in a decade, while some parts of the US see insect activity begin 20 days earlier than 70 years ago. Most animal and plant species depend on heat buildup in spring to initiate flowering, breeding, hatching and releasing insect eggs. The reshuffling of the season’s start risks throwing delicately poised interactions off-kilter, such as birds setting off on migration early only to find a food source isn’t quite ready for them yet.

British scientists looked at half a century’s worth of UK data to find that aphids are now appearing a month earlier then they used to. This is because of rising temperatures. Meanwhile, birds are laying their eggs a week earlier. The aphids aren’t necessarily growing in number, despite their elongated season, but their earlier appearances means they are targeting plants that are younger and more vulnerable.

“There’s good evidence here in the UK that under climate change things are warming up early, so we’ve got all these bees coming out early but not the flowers, because obviously the day length isn’t changing,” says Simon Potts, a bee expert at the University of Reading. “We’re getting this decoupling between pollinators and the plants and that’s starting to mess up all these very delicate, very sophisticated food webs.”

Warmer Britain is a welcome development for some insects. Insects such as the violet carpenter Bee and the camel Cricket have crossed the Channel to establish themselves. Meanwhile, native butterflies such as the marbled White are overcoming population declines by a climate-assisted march towards cooler climes. Wild orchids and other flowers are also heading north.

These adaptive techniques won’t make much sense if climate change alters the properties of plants, making them less useful as food sources for insects. Scientists have discovered that CO2 can lower the nutritional value of plants and provide insects with empty calories without essential nutrients like zinc or sodium. A Kansas prairie study found that grasshopper numbers are declining by approximately 2% annually. Researchers were confident enough to rule pesticide use and habitat loss out as possible causes. They concluded that the climate emergency was causing grasshopper starvation.

Climate change is causing insects to become malnourished. It may also alter the plants’ scents. Pollinators searching for food will note the colour and number of flowers as well as the plant’s scent, with bees able to recall a fragrance and associate it with certain plants and their nectar content. Scientists measured the scent molecules of rosemary in shrubland near Marseille in France. They found that stressed plants emit a different fragrance, which discouraged domesticated bees. The climate crisis is putting more pressure on plants, causing them to be more susceptible to drought and high heat. This could make them unappealing to insects.

This alteration in plants could be, at least for insects, the most severe symptom of climate change.

NHowever, not all insects will be affected by a warming planet. As with all realignments there are winners as well as losers. Our attention is drawn more to the thoughts of hordes marauding insects unassisted by global warming than to a few scientists worrying about a declining desert moth. 2020 saw the worst plague of locusts east Africa has seen in decades. The Horn of Africa was hit hard by heavy rainfall in the previous year. This led to the reproduction of locusts. Both climate change and increased heat are thought to increase locust numbers. Kenyan farmers watched helplessly as locusts descended to decimate their corn, sorghum and crops. Separate, massive swarms broke out in central and western India, consuming land at a rate never seen in a generation.

A warmer world will likely bring an array of pathogens and insect pests to attack wheat, soya bean, and other crops. A group of American researchers calculated that yields of the three most important grain crops – wheat, rice, and corn – lost to insects will increase by as much as 25% per degree Celsius of warming, with countries in temperate areas hit the hardest. Crop pests also tend to thrive in simplified environments that have been stripped of their predators – another legacy of monocultural farming practices.

We will see more of the brilliantly colored emerald-ash borers in American suburbs. They are a species of brightly green beetles that are native to Asia. They were introduced to America after a few of them managed to cling to some wooden packaging. The rapacious insects have decimated hundreds and millions of ash trees in North America and are now spreading to eastern Europe. Milder winters mean that the pests can spread further north, causing even more destruction.

Domestic environments will see an increase in unwanted insects. One estimate suggests that houseflies populations could more than double by 2080. This is due to changes such as temperature, humidity, rainfall, and other factors. But while houseflies can cause illness through the transfer of waste on to food, at least they aren’t major vectors of deadly conditions.

It is worrisome, therefore, that there’s an expansion under way of mosquitoes.

The freezing temperatures are known to kill mosquito eggs. This means that insects can conquer new territories due to the planet’s heat. There have been several outbreaks of dengue in France, Croatia, Italy, and Greece in the last decade. These incursions are likely vanguards. The Mediterranean region is already partly tropical and heat and moisture will continue to build. As a result, the central region of Europe and the UK’s southern regions will be within striking distance of a fearsome group of newcomers. “If it gets warmer we could get West Nile. Malaria could come back, too,” says Simon Leather, a British entomologist. “We could see a real change in terms of human health problems.”

Mosquitoes are, based on the number of human deaths, the most dangerous animals on Earth. Yet, in our rush to eradicate them, we often resort to weapons that cause collateral harm. The chemical compound DDT was developed for widespread anti-mosquito use – before mosquitoes developed resistance and the chemical’s pernicious impact on other wildlife led to its ban. A newer replacement, naled, an organophosphate, is being used to spray mosquito habitat, despite the fact that it is toxic for bees, fish, and other creatures. If our fears of a heat-loving invasion were to be fulfilled by one animal, it would be the Asian gianthornet.

You might have heard it referred to as a “murder” hornet. The large, thumb-sized hornet looks like a cartoon supervillain with its tiger-striped stomach, large burnt orange-coloured head, teardrop eyes that look like a demon Spider-Man, and vicious mandibles. Despite all the public outrage, murder hornets don’t kill people. They kill honeybees. The hornets linger outside beehives and brutally decapitate emerging worker honeybees. They then feed the larvae their body parts and dismember them.

This carnage can continue for hours, until a hive is destroyed completely. The crime scene is marked by thousands upon thousands of dead bodies. Some bees will fight back in some areas. Bees in the hornets’ native range have evolved a defensive tactic whereby a mob of bees will hurl themselves at a hornet that enters the hive, covering the invader in a ball-like mass and then vibrating their flight muscles to generate so much heat, up to 47C, that the hornet is roasted alive. However, honeybees in North America and Europe are not used to the hornet, and are almost helpless when faced with the slaughter.

The Asian giant hornet (or as its name suggests) is a hornet.Vespa mandariniaIt is native to the forests of south-east Asia’s mountain foothills. It is often mixed up with its Asian cousin, the Asian hornet.Vespa velutina), which has found its way to Europe and dismembered so many honeybees in the UK and France that bee-keepers have fretted over the viability of colonies already under stress from varroa mites and pesticides. Vespa mandariniaMeanwhile, he has launched an attack on the western coast North America, most likely by riding along on cargo shipping.

In August 2019, three confirmed specimens were found by Canadian authorities on Vancouver Island. A second specimen was discovered further south, close the US border. The species was again spotted in the US in December, 12 miles south in the state Washington. After being stung by hornets a few times, one beekeeper set fire to the entire colony. Another queen hornet, located 15 miles south-west from the next find, suggested that there was either an influx from overseas, or a vigorous dispersal of the hornets.

By May 2020, with the hornet appearing to have gained a decent foothold on the west coast, the situation had attracted the attention of the New York Times, which ran a story headlined “‘Murder Hornets’ in the US: The Rush to Stop the Asian Giant Hornet.” Climate change could help turbocharge the pace of the hornet’s advance, similar to the astonishing travels of the Asian hornet in France, where it has moved at nearly 50 miles a year since arriving in the early 00s and is now found in the Alps.

It’s natural to get squeamish over the idea of a squadron of murderous hornets or the idea that those ever-durable cockroaches will march on despite the surging heat. The most frightening aspect of all this is the climate breakdown itself. This is an existential threat that we have created upon ourselves and all living creatures, despite decades worth of increasingly frantic warnings.

But as we’ve reacted so grudgingly and ponderously to the menace of flooding, storms and droughts that can spark civil unrest and even wars, what hope is there that the plight of insects will spur us on? It is better to make a concerted effort in order to restore insect-friendly habitats that are complex and interconnected. This will help to reduce the impact of climate change. Although climate breakdown can often feel like a drawn-out, almost imperceptible rearrangement that far-off generations will have to deal with, it is also punctuated with lacerating reminders that it’s already well under way.

This is an edited excerpt from The Insect Crisis: The fall of tiny empires that rule the world, published by Atlantic on 20 January.