Insects have declined by 75% in the past 50 years – and the consequences may soon be catastrophic. Biologist Dave Goulson reveals the vital services they perform

I have been fascinated by insects all my life. One of my earliest memories is of finding, at the age of five or six, some stripy yellow-and-black caterpillars feeding on weeds in the school playground. I put them in my empty lunchbox, and took them home. Eventually they transformed into handsome magenta and black moths. This seemed like magic to me – and still does. I was hooked.

In pursuit of insects I have travelled the world, from the deserts of Patagonia to the icy peaks of Fjordland in New Zealand and the forested mountains of Bhutan. I have watched clouds of birdwing butterflies sipping minerals from the banks of a river in Borneo, and thousands of fireflies flashing in synchrony at night in the swamps of Thailand. At home in my garden in Sussex I have spent countless hours watching grasshoppers court a mate and see off rivals, earwigs tend their young, ants milk honeydew from aphids, and leaf-cutter bees snip leaves to line their nests.