One of the classic moments in the Simpsons comes when the venal TV anchorman Kent Brockman sees on his screen an ant crawling across a lens and assumes at once that this is not a negligible terrestrial arthropod but a giant alien descending from space that will become one of “our new insect overlords”, a species to which he instantly and publicly pledges allegiance. The joke hinges on the idea that in real life ants are inconsequential compared with human beings. The world, we feel, could get on perfectly well without them, and still better without mosquitoes or any number of other creepy crawlies.

This confidence is quite as mistaken as Kent Brockman’s grovellings. Insects form the greatest part of animal life on Earth, and almost every other kind of animal depends on them – directly or indirectly. They pollinate plants and nourish animals, especially birds. In turn, everything that relies on these plants or animals depends on the insects. And the whole intricate web of interdependent exploitation is collapsing, and has been for decades. We ourselves are part of this web, in the long run quite as much dependent as exploitative.

On the island of Puerto Rico, a rainforest preserved for centuries from human intervention shows a terrifying drop in the abundance and variety of insects. Forty years ago, there were 60 times as many insects on the forest floor as can be trapped today. The bird and lizard species that feed on insects have also been hit, if not to the same extent, falling by between a third and a half over the same period.

The same trend is apparent in German nature reserves, where the number of insects appears to have dropped by about 75%; and these are results from places deliberately preserved, so far as possible, from human intervention. The collapse of insect life is obvious to anyone who looks in Britain – butterflies, bees and even the millions of chironomid midges that used to form plumes like smoke around the trees along the shores of reservoirs are all now mostly a memory. Car windscreens and headlights are no longer thickly speckled after any long journey.

The causes of this global decline seem to vary with latitude. But they are all, in one way or another, the product of human activity. In the temperate regions insect populations are more adaptable to fluctuations in temperature, but insects must contend with the mass use of pesticides across the bleak monocultures of industrial agriculture, as well as the generalised pollution of the air and water. In the rainforest, where the pattern of losses across species and over time shows that there must be some single vast factor acting on the whole ecosystem, it appears that the main driver is simply the climate catastrophe. The consequences of this collapse lend still more urgency to political efforts to slow and eventually halt climate change; but even as individuals we can follow Candide’s advice and cultivate our gardens so insects can thrive there.