A shard of iridescent green landed on my arm: a momentary gift of a jewel, highly polished, almost absurdly beautiful in the sun's rays. Always a slightly surreal moment, when you cease to be an intruder in the landscape and become a feature of it.

I am not always delighted when an insect uses me as a landing ground, but I was happy enough to make the acquaintance of this thing: maybe half an inch long, and with a bright red bum. He gave me plenty of time to examine him, and then, when I blew a brief gale on to his back, he opened his wing-cases and flew.

A beetle, then. For beetles have a unique arrangement: their backs are covered in crunchy double-doors, which they open to release the much flimsier wings when they fly.

I went home and looked him up: common malachite, or if you prefer, red-tipped grass beetle. But anyway, Malachius bipustulatus, as described by Linnaeus in 1758. A fine thing, a rather lovely thing, red tips to shining green wing-cases. The male transfers sex hormones to the female with his antennae as a kind of foreplay. Both sexes, when alarmed, put predators off by making a stink: two elegant adaptations, absolutely characteristic of the depth, the range, the imagination, the virtuosity of beetle-kind.

Look for these malachites yourself: you can find them on flowers of open structure where they take pollen, nectar and other insect visitors to the same flowers. The daisy, rose and carrot families are their preference. You can find anything, you can find almost everything, once you start looking at beetles.

We can't work it out

It began with that big book of 1758, Linnaeus's Systema Naturae. Since then, 350,000 species of beetles have been described. That works out at nearly four new species per day - so we can say with some confidence that we really have scratched the surface. Estimates of the total number range between five and eight million.

But even if we stick with the beetles we already know about, they go far beyond the limits of the human imagination. Beetles are like stars in the sky: that little bit too numerous for us to deal with in comfort. Every fifth species of known living things - things like oak trees and lemurs and mushrooms and albatrosses - is a beetle. Every tenth species is a weevil, and that's just one sort of beetle.

Beetles are there to bewilder, and they can bewilder in any way you choose. Take just size: there are species of beetles that can, unlike a camel, comfortably crawl through the eye of a needle; Hercules and Goliath beetles can comfortably cover the palm of your hand. Though I'm not sure how comfortable I'd be.

In 265 million years of existence, beetles have managed to fill every habitat bar the sea and the poles. You find them in the driest deserts, at the top and at the bottom of rainforests. You find them in ponds: whirligig beetles have split eyes: one half for looking through air and one half for looking through water.

They have worked out every imaginable way of earning a living. There are beautiful beetles and dull beetles, scary beetles and cuddly beetles (like ladybirds). There are straightforward functional beetles, there are beetles of baroque excess. There are black and brown beetles, there are beetles of fantastic and glorious colour. There are beetles that stand out from the world: there are beetles so intricately camouflaged as to be invisible. You think of a way of life: a beetle got there first.

We're nowhere, man

Perhaps beetles are life's greatest triumph. We are accustomed to skewing every way we look at the world to show humans to the best possible advantage: but perhaps the resilience and the brilliance of any form of life lies in its ability to diversify: to create an enormous and sublimely resilient adaptive radiation.

Beetles are a comparatively low level of classification. Beetles make up the order of coleoptera, just as we belong to the order of primates. There are three or four hundred species of primates, and there are unlikely to be many more to discover. We have been comprehensively outcompeted.

Beetles are a living sermon on human failure. We primates have failed to match the beetles for diversity, and we have failed in our noble attempt to count them all. In 250 years, we are nearly a tenth of the way there: in three millennia or so, we may have been getting close - particularly as we are destroying God knows how many undiscovered species every day.

But here's a thought. What odds do you give for the continuation of the human species, or any other primate, in 3,000 years' time? But it's a bang-on certainty that there'll still be beetles. Look on a common malachite: feel humble in his presence.

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