The phrase “they come in all shapes and sizes” could have been coined just for the Coleoptera — the beetles. At a fragile 0.325mm long, the Colombian featherwing (Scydosella musawasensis) has a good claim to being one of the smallest free-living insects in the world, and is tinier than many single-celled creatures. At the other end of the spectrum, the obviously named titan beetle, a huge Brazilian longhorn that can snap a pencil in its jaws, reaches 167mm – about 500 times the size.
Coleoptera range from the narrow sylph-like elegance of the mould beetle (Adistemia watsoni) crawling up the musty wall of a museum store-room, to the burnished brass bauble of the golden leaf beetle (Chrysolina banksi), cumbersomely crawling over the black horehound plant it feeds on.
They occur from seashore to mountain top. Around the south and west coasts of Britain, the tiny pale ground beetle (Aepus robinii) survives in silt-filled cracks in seashore rocks, and is covered up by the tide twice a day. Meanwhile the rainbow leaf beetle (Chrysolina cerealis) is only known (in Britain at least) from Snowdon in Wales, where its chubby larvae feed on a few clumps of stunted thyme growing on the windswept mountainsides.
Beetles (or more often their larvae) eat anything from wild and garden plants (too many gardeners revile the poor old lily beetle (Lilioceris lilii), to pollen, algal film, leaves, fruits, nuts, stems, roots, dung, carrion, rotten wood, construction timber, harvested grain, stored food, other invertebrates, and each other. They live in water, up trees, in the soil, in ant nests, in bee burrows, in our homes; they visit flowers, they patrol leaves, they fly and bump at the lighted window of a late summer evening. Platypsyllus castoris lives in the pelts of beavers, scraping a living from dead skin and sebaceous secretions. Beetles live everywhere and do everything.
Across the globe it’s anybody’s guess how many beetles are out there awaiting discovery. About half a million beetle species are identified, described and catalogued in the world’s museums and reported in about 250 years of erudite scientific literature, but in 1982 a philosophical bombshell rocked the entomological establishment. Insecticide fogging experiments in the Panamanian forests brought down a rich rain of known and unknown species into the collecting bins and ground sheets laid out below. Extrapolation of the 1,200 beetle species from one species of tropical tree suggested there were actually 12 million beetle species on Earth.
More abstruse mathematical and statistical calculation has made things worse, with some now arguing that there are actually 33 million beetle species here. This was getting crazy – rather than nearing consensus, the scientists could not agree even to within an order of magnitude.
In the British Isles about 4,000 beetle species range from the not-quite-so-tiny but equally tongue-twisting Baranowskiella ehnstromi at 0.45mm, up to the iconic stag, Lucanus cervus, which reaches 55mm not including the male’s imposing antler-style jaws. In the middle is a huge centre ground of ladybirds, leaf beetles, chafers, ground beetles, rove beetles and longhorns. They perfectly illustrate the huge diversity in shape, form, life history, ecology and behaviour of this wonderful order of insects.
So why are beetles not as universally popular with naturalists as, say, butterflies and moths, hoverflies, dragonflies, bumblebees and grasshoppers? Despite the prominence of the group from a biological perspective, beetles are still the preserve of the expert, or so it seems. The identification of many species rests on the analysis of obscure comparative details only visible down the microscope. Guides and monographs are highly technical and littered through with obfuscating jargon. In his 1872 essay The Poet at the Breakfast Table, Oliver Wendell Holmes has his self-important entomologist mock the childish simplicity of moths and lacewings before the serious complexity and obvious importance of the beetles – “Lepidoptera and Neuroptera for little folks; and Coleoptera for men, Sir!”
Modern coleopterists might not proclaim it in such pompous tones, but an in-depth study of even Britain’s impoverished beetle fauna sometimes seems a puzzle beyond patience – the hard work of many lifetimes. But beetles are not only everywhere, in every shape, size and form, they can also be found all year round. They indicate freshwater quality, ecological continuity of threatened habitats like ancient woodlands and chalk downland; they are an excellent measure of local conservation effort and regional biodiversity. It is a beetle (the harlequin ladybird, ) which offers the best model and most studied example of a newly colonising species spreading across the British Isles, since it arrived in Essex in 2003. Beetles are already at the forefront of climate change research as Mediterranean species invade and cold-adapted northern and mountain-dwelling species are edged further north, or further up mountainsides.
If an alien civilisation arrived on Earth and, with limited time and limited resources, wanted to understand how life here operates, all it need do is to study beetles and dismiss everything else as sampling error. Beetles are, without any doubt, the most important organisms on the planet.
• Richard Jones is an entomologist and writer. His latest book, Beetles, is published by William Collins.
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