Most of us are familiar with the story of the passenger pigeon, so numerous in the late 1700s that flocks of billions of birds darkened the sky for hours as they passed. Humans exterminated them in a little over 100 years, the last wild passenger pigeon being shot in 1901. In contrast, few have ever heard of the Rocky Mountain locust, but its story is similar. Once very common, swarms would occasionally erupt from their core range in the eastern Rocky Mountains, spreading eastward across the Great Plains. In 1875, a particularly large swarm of this grasshopper was estimated to contain perhaps 12.5 trillion individuals, possibly the most common organism ever witnessed by man. Within just 28 years it was extinct, the last one being recorded in 1902. The cause of this most dramatic of extinctions is unclear, but it seems that the core breeding ground of this species was river valleys in Montana and Wyoming, where the locust laid its eggs in sandy soils. These areas were fertile and easily cultivated, so were among the first settled and ploughed by farmers, destroying the eggs of the insect.
The contrast between public awareness of the fate of the passenger pigeon and that of the Rocky Mountain locust reflects a more general bias. We tend to identify with and care about large creatures (mammals and birds in particular), while paying little or no attention to the much smaller creatures, the insects and their kin. Children are often fascinated by insects, but sadly they usually grow out of this, and the first reaction of many teenagers or adults to anything that buzzes or scuttles near them is likely to be an attempt to swat it or stamp on it. Even the common names we give insects, such as “bugs” and “creepy-crawlies,” reflect this negative attitude.
I fell in love with insects when I was just 5 or 6 years old. I never grew out of my childhood obsession, and I have been lucky enough to make a career out of studying their often weird and wonderful lives. My mission is to persuade others to care for and respect them, for we all need insects, whether we know it or not. The 1.1 million known species of insect comprise more than two-thirds of all known species on our planet. Insects pollinate roughly three-quarters of the crops we grow, including most of our fruit and vegetables, such that many of us would starve without them. They also pollinate the large majority of wildflowers; recycle dung, leaves and corpses; help to keep the soil healthy; control pests; and much more. They are food for numerous larger animals such as most birds, freshwater fish, frogs and lizards. Ecosystems would grind to a halt without insects.
It should thus be of concern to all of us that insects are in decline. Every year there are slightly fewer butterflies, fewer bumblebees — fewer of almost all the myriad little beasts that make the world go round. Estimates vary and are imprecise, and many insects, particularly those in the tropics, are simply not being systematically counted by anyone, but the data we do have overwhelmingly suggest a pattern of decline. For example, in Germany, the biomass of flying insects fell by 76 percent in the 27 years to 2016. In the U.S., monarch butterfly numbers have fallen by 80 percent in 25 years. In the U.K., butterflies have halved in abundance since 1976, when I was 11 years old. These changes have happened in our lifetimes, on our watch, and they continue to accelerate.
My youngest son is now 11; he is growing up in a world where butterflies are half as common as they were when I was his age. How many butterflies will his children ever see?
The famous American biologist Paul Ehrlich likened loss of species from an ecological community to randomly popping out rivets from the wing of a plane. 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. In his analogy, insects are the rivets that hold ecosystems together.
What is driving the decline of insects? There are many factors, but clearly the industrialization of farming, particularly the move toward large-scale monoculture cropping dependent on a blizzard of pesticides is playing a major role. In 1962, three 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. The problems with pesticides and fertilizers Carson highlighted have become far more acute. Some of these new pesticides, such as neonicotinoids, are thousands of times more toxic to insects than any that existed in Carson’s day. The U.S. in particular has an especially gung-ho attitude to pesticides, with U.S. farmers accounting for nearly 20 percent of all global use. About one-quarter of the pesticides used in the U.S. are now banned in the European Union due to concerns over risks to human or environmental health. The U.S. allows several pesticides now banned in China and Brazil, neither of which is famed for its sensitive approach to environmental protection.
The Rocky Mountain locust may be extinct, but other grasshoppers are still common in the same area, and occasionally there are outbreaks that spill out into surrounding states. The grasshoppers eat grass, competing with livestock and hence impacting ranchers. One such outbreak occurred in the summer of 2021, prompting the federal government to fund aerial spraying of about 1 million acres of rangeland in Montana and neighboring states with an insecticide, diflubenzuron. Those responsible for this decision argue that the chemical does little harm to other insects, but this is clearly nonsense, since elsewhere the same chemical is applied commercially to kill various butterflies, moths, beetles, flies and termites, and it is highly toxic to bumblebees. The chemical is even toxic to many plants. So what is the collateral damage from this carpet-bombing of the landscape? There are tens of thousands of native insect species in Montana; this spraying will kill untold trillions of individual insects (including monarch butterfly caterpillars). This in turn will impact the functions that these insects perform; fewer pollinators for crops and wildflowers, fewer insects for birds to eat. Grasshoppers and other insects are an essential protein source for chicks of many birds such as the endangered greater sage grouse. In turn, the birds help to keep the grasshoppers in check. If the birds decline further, along with other natural enemies of the grasshoppers, future outbreaks will be worse, and more insecticide will be sprayed. It is a self-defeating war on nature that can never be won. I find myself wondering if the crop duster pilots play “Ride of the Valkyries” on their cockpit radio, while muttering “I love the smell of insecticide in the morning.”
Pesticides are not the only problem insects face in the modern world. Ongoing habitat loss — particularly of tropical forests — and the spread of invasive species and non-native insect diseases are all taking their toll. Light pollution attracts countless night-flying insects to bash themselves to death on artificial lights, and disrupts the ability of insects to judge day length and emerge from hibernation at the correct time of year. Many soils have been degraded, rivers choked with silt and polluted with chemicals or simply so much water extracted that they run dry. Climate change, a phenomenon unrecognized in Rachel Carson’s time, is now threatening to further ravage our planet. The recent failure of COP26 to achieve any meaningful international progress on tackling climate change means that in the future, insects will have to cope with more frequent droughts, wildfires, floods and storms. It is death by a thousand cuts.
Our planet has coped remarkably well so far with the blizzard of changes we have wrought, but we would be foolish to assume that it will continue to do so. A relatively small proportion of species have actually gone extinct so far, but almost all wild species now exist in numbers that are a fraction of their former abundance, subsisting in degraded and fragmented habitats and subjected to a multitude of ever-changing man-made problems. We do not understand anywhere near enough to be able to predict how much resilience is left in our depleted ecosystems, or how close we are to tipping points beyond which collapse becomes inevitable. In Paul Ehrlich’s “rivets on a plane” analogy, we may be close to the point where the wing falls off.
To learn more about insect declines and what you can do to help reverse them, read Silent Earth by Dave Goulson, published by HarperCollins in 2021.