SOURCE: The Guardian
DATE: July 25, 2021
SNIP: In 1963, two years before I was born, Rachel Carson warned us in her book Silent Spring that we were doing terrible damage to our planet. She would weep to see how much worse it has become. Insect-rich wildlife habitats, such as hay meadows, marshes, heathland and tropical rainforests, have been bulldozed, burned or ploughed to destruction on a vast scale. The problems with pesticides and fertilisers, she highlighted, have become far more acute, with an estimated 3m tonnes of pesticides now going into the global environment every year. Some of these new pesticides are thousands of times more toxic to insects than any that existed in Carson’s day. Soils have been degraded, rivers choked with silt and polluted with chemicals. Climate change, a phenomenon unrecognised in her time, is now threatening to further ravage our planet. These changes have all happened in our lifetime, on our watch, and they continue to accelerate.
Few people seem to realise how devastating this is, not only for human wellbeing – we need insects to pollinate our crops, recycle dung, leaves and corpses, keep the soil healthy, control pests, and much more – but for larger animals, such as birds, fish and frogs, which rely on insects for food. Wildflowers rely on them for pollination. As insects become more scarce, our world will slowly grind to a halt, for it cannot function without them.
Insects have been around for a very long time. Their ancestors evolved in the primordial ooze of the ocean floors, half a billion years ago. They make up the bulk of known species on our planet – ants alone outnumber humans by a million to one – so if we were to lose many of our insects, overall biodiversity would of course be significantly reduced. Moreover, given their diversity and abundance, it is inevitable that insects are intimately involved in all terrestrial and freshwater food chains and food webs. Caterpillars, aphids, caddisfly larvae and grasshoppers are herbivores, for instance, turning plant material into tasty insect protein that is far more easily digested by larger animals. Others, such as wasps, ground beetles and mantises, occupy the next level in the food chain, as predators of the herbivores. All of them are prey for a multitude of birds, bats, spiders, reptiles, amphibians, small mammals and fish, which would have little or nothing to eat if it weren’t for insects. In their turn, the top predators such as sparrowhawks, herons and osprey that prey on the insectivorous starlings, frogs, shrews or salmon would themselves go hungry without insects.
The loss of insect life from the food chain would not just be catastrophic for wildlife. It would also have direct consequences for the human food supply. … 87% of all plant species require animal pollination, most of it delivered by insects. The colourful petals, scent and nectar of flowers evolved to attract pollinators. Without pollination, wild flowers would not set seed, and most would eventually disappear. There would be no cornflowers or poppies, foxgloves or forget-me-nots. But an absence of pollinators would have a far more devastating ecological impact than just the loss of wild flowers. Approximately three-quarters of the crop types we grow also require pollination by insects, and if the bulk of plant species could no longer set seed and died out, then every community on land would be profoundly altered and impoverished, given that plants are the basis of every food chain.
Insects are also intimately involved in the breakdown of organic matter, such as fallen leaves, timber and animal faeces. This is vitally important work, for it recycles the nutrients, making them available once more for plant growth. Most decomposers are never noticed. For example, your garden soil – and particularly your compost heap, if you have one – almost certainly contains countless millions of springtails (Collembola). These minute, primitive relatives of insects, often less than 1mm long, are named for their clever trick of firing themselves as high as 100mm into the air to escape predators. This army of minuscule high-jumpers does an important job, nibbling on tiny fragments of organic matter and helping to break them up into even smaller pieces which are then further decomposed by bacteria, releasing the nutrients for plants to use.
The American biologist Paul Ehrlich likened the loss of species from an ecological community to randomly popping out rivets from the wing of an aeroplane. Remove one or two and the plane will probably be fine. Remove 10, or 20 or 50, and at some point that we are entirely unable to predict, there will be a catastrophic failure, and the plane will fall from the sky. Insects are the rivets that keep ecosystems functioning.
In October 2019 a different group of German scientists published their findings from a study of insect populations in German forests and grasslands over 10 years from 2008 to 2017. The study’s results were deeply troubling. Grasslands fared worst, losing on average two-thirds of their arthropod biomass (the insects, spiders, woodlice and more). In woodlands, biomass dropped by 40%.
What about elsewhere? Is there something peculiar going on in Germany? It seems highly unlikely. Perhaps the best-studied insect populations in the world are the UK’s butterflies. They are recorded by volunteers as part of the Butterfly Monitoring Scheme, the largest and longest-running scheme of its kind in the world. The trends it reveals are worrying. Butterflies of the “wider countryside” – common species found in farmland, gardens and so on, such as meadow browns and peacocks – fell in abundance by 46% between 1976 and 2017. Meanwhile, habitat specialists, fussier species that tend to be much rarer, such as fritillaries and hairstreaks, fell by 77%, despite concerted conservation efforts directed at many of them.
Worldwide, although the bulk of insect species – the flies, beetles, grasshoppers, wasps, mayflies, froghoppers and so on – are not systematically monitored, we often have good data on population trends for birds that depend on insects for food, and these are mostly in decline. For example, populations of insectivorous birds that hunt their prey in the air (ie the flying insects that have decreased so much in biomass in Germany) have fallen by more than any other bird group in North America, by about 40% between 1966 and 2013. Bank swallows, common nighthawks (nightjars), chimney swifts and barn swallows have all fallen in numbers by more than 70% in the past 20 years.
In England, populations of the spotted flycatcher fell by 93% between 1967 and 2016. Other once-common insectivores have suffered similarly, including the grey partridge (-92%), nightingale (-93%) and cuckoo (-77%). The red-backed shrike, a specialist predator of large insects, went extinct in the UK in the 1990s. Overall, the British Trust for Ornithology estimates that the UK had 44m fewer wild birds in 2012 compared with 1970.
All the evidence above relates to populations of insects and their predators in highly industrialised, developed countries. Information about insect populations in the tropics, where most insects live, is sparse. We can only guess what impacts deforestation of the Amazon, the Congo, or south-east Asian rainforests has had on insect life in those regions. We will never know how many species went extinct before we could discover them.