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The humble beetle is a familiar sight in every British garden. Not surprising, since there are more than 4,000 species in the UK! As nutrient recyclers, they return organic matter to the earth and contribute to soil fertility. Worldwide, the beetle population totals 350,000 species. Around 40% of insect species in the UK are beetles, ranging from extremely tiny bugs, to large, brightly coloured beetles such as stag beetles and ladybirds. Any insect in the beetle family has three main parts to its body (the head, abdomen and thorax), six jointed legs and an exoskeleton. It also has a pair of antennae and compound eyes, consisting of a curved array of microscopic lenses. Otherwise known as Coleoptera, beetles have been described by scientists as "the most important organisms on the planet". Living everywhere from ponds and seashores to mountain tops and trees; they can survive in water, in the soil, in ants' nests, in beehives and all over our homes. Some can fly and visit flowers; others simply patrol our garden, crawling about the leaves; one species, the Platypsyllus Castoris, lives its whole life on beavers, eating dead skin cells. Beetles can live anywhere and eat almost anything including wild and garden plants, pollen, algae, fruits, nuts, leaves, roots, stems, wood, dung, carrion, stored food, grain, other invertebrates and even each other! They come in all shapes and sizes, from the tiny 0.325mm-long Colombian feather wing to the mighty 16.7cm Brazilian longhorn. In the UK, the smallest beetle is the Baranowskiella Ehnstromi at 0.45mm long and the biggest is the stag beetle, or Lucanus Cervus, which grows to 5.5cm long, not including the male's antler-like jaws. This amazing order of insects perfectly illustrates a huge diversity in shape, ecology and behaviour.   Why are beetles so important? As they live in such a wide variety of habitats, they can indicate the quality of freshwater and ensure the ecological continuity of habitats such as ancient woodland and chalk downland. The presence of beetles is a good indicator of regional biodiversity and local conservation efforts. One species of beetle has been used as the best model and most researched example of how a new species colonises across a nation. The harlequin ladybird has been steadily spreading across the UK since it first arrived in Essex in 2003. This tropical long-horned beetle, originally from Asia, is now one of the most common ladybirds in Britain, particularly around our towns and gardens. It is known for controlling the aphid population. Beetles are now at the forefront of research into climate change, as more Mediterranean species are invading countries that were once too cold and are adapting to global warming. Mountain-dwelling species of beetle are living further up the mountainsides, where once it would have been too cold.   How much do we know about beetles? The study of beetles all over the world has been documented in scientific literature dating back around 250 years. The name for people who study beetles is "coleopterists". A complex field, there are so many different species. In fact, it is estimated there are still thousands of species of beetle that haven't even been discovered yet. Scientific research (known as "fogging" experiments) in the forests of Panama brought down a rain of known and new beetle species into groundsheets and collecting bins below. Examination of the beetles from one variety of tropical tree revealed it was home to around 1,200 different species of beetle! As there are so many species, including the most minute that are less than 1mm long, scientists admit it is almost impossible to say exactly how many different types live on our planet. The generally quoted figure of 350,000 species is the most conservative estimate. Some research, based on finds in tropical forests of new species, suggests there may be up to 12 million beetle species on earth!   What beetles live in the UK? Britain has some spectacular and beautiful beetles. One of the most amazing is the rainbow leaf beetle, with its metallic bands of blue, green, gold and red. Around 8mm long, it is a rare species, found only on Mount Snowdon in Wales. It is one of a handful of UK beetle species that is protected by law, due to its rarity. The thick-legged flower beetle is another unusual species, as it is a bright metallic green colour. Measuring up to 10mm long, it gets its name from the large bulges on the males' thighs. You can still spot them in your garden, as they are around between April and September. They are widespread in many areas of England. You can see thick-legged flower beetles between April and September in gardens, flower meadows and waste ground. Useful pollinators, they move from flower to flower on roses, poppies, cornflowers, daisies and more. The minotaur beetle is another species you might spot in autumn. The glossy black male has three spectacular prongs sticking out from the centre of its body, resembling mini horns, like you would find on a bull. The horns are used for competing for females and defending their nest. The minotaur is a member of the earth-boring dung beetle family, known as Geotrupidae. It drags animal droppings to its nest to feed the larvae. This plays an important role in recycling nutrients and waste. The UK Coleoptera organisation is encouraging people to record and submit beetle sightings at www.coleoptera.org.uk for its UK Beetle Recording project. The aim is to establish a comprehensive database for studies. All records will be available for general use via the National Biodiversity Network Gateway.   Building a bug hotel If you want to encourage beetles into your garden, consider building a "bug hotel". The RSPB says it's a simple job that can be completed within a couple of hours. It's a great way to use all your garden waste and "odds and ends" to provide a safe hideaway for beetles. It could also provide a shelter for hedgehogs and toads, as well as a wide variety of insect life. Autumn is a good time to build the bug hotel, as there are more natural materials around, such as straw, dry grass and hollow plant stems. You can make a very simple one, using old wooden pallets to provide a strong framework that can be up to one metre high. Put some ordinary house bricks on the ground as a base and add a few layers of pallets, making sure they are secured with either nails, or further bricks on top, to stop them from blowing away in strong winds. Fill each layer with all kinds of waste including wood, dried plant stems, leaves, stones, tiles, sticks, straw, corrugated cardboard, drilled logs and just about anything else you can find. Then, go out and check it regularly and see which beetles have arrived. This could help you to take part in Coleoptera's nationwide beetle recording project. It also provides an interesting activity for kids, especially in the autumn. Whatever the weather, put on some warm clothing and go outside to see who has checked into your bug hotel!