Subtitles section Play video Print subtitles OK, now here's a question. What's the biggest living organism on the planet? A whale? A redwood tree? Arguably it's armillaria, a huge honey fungus living in a forest in Oregon, USA. It covers over nine square kilometres and is thought to be at least 2,400 years old. Oh, and it glows in the dark. Mind blown? What if we also told you that other types of fungi can absorb oil spills, control insects' brains and that fungi in general are essential to all terrestrial life on Earth? And there's still so much we don't know - more than 90% of the fungi in the world are currently unknown to science. You could say there's mush-room for learning. Now that we've got that terrible pun out of the way, we can take a closer look at some fascinating facts that will make you a real fun-guy at parties. Sorry. If you think of mushrooms as vegetables on your pizza, you're not alone, thanks to the Victorian botanists who classified fungi with plants. In fact, fungi are neither plant nor animal. They are in a kingdom of their own, but are genetically much closer to animals. The genetic code of a mushroom has more in common with ours than a potato's. Maybe don't mention that to your vegan friends. Fungi also have the ability to control other organisms. While some species of fungi break down dead leaves and wood, like the helpful housemate who always remembers to take the bins out, other fungi are mycorrhizal, they plug into the root tissue of plants and pass precious nutrients between them. This process forms a dense fungal network called a mycelium. Soil often contains masses of these mycelial threads connecting different plants, like fibre-optic cables. In woods, the network is known as the wood-wide web because plants use it to communicate with one another. In a fertile pasture, the fungi feeding on plants below ground can be many times heavier than the cows eating the grass above it. Some fungi get other species to do the work for them. The Leucoagaricus uses chemical signals to 'employ' leaf-cutter ants. The ants work together to form a supply chain that can deliver up to 60,000 leaf fragments an hour to the fungus. In return, it produces miniscule ant-sized mushrooms to feed them. Other fungi employ more gruesome methods. Cordyceps infiltrate their insect host - for example ants or beetles - and control their brains, forcing them to climb up high, and then bursting out of their bodies to scatter their spores to the wind. Talk about evil genius. Not content with insect mind-control, some types of fungi can trouble humans, causing irritations like athlete's foot, as well as the more deadly histoplasmosis. Ergot, a fungus that grows on wheat and rye, can literally send you mad - eating bread made from affected flour is likely to have contributed to mass hallucinations in medieval Europe. And you don't have to be a seasoned forager to know that some species of fungi are highly toxic. If I were you, I'd avoid anything with an intimidating biker-gang name like Autumn Skullcap or Destroying Angels. While fungi can, in some cases, be extremely dangerous, they are also an invaluable resource. For a start, fungi produce life-saving medicines such as penicillin. Yeast is a fungus, without which we'd have no bread, wine, beer or cheese. Even Quorn is made from a fungus. Basically, without fungi there would be no middle-class dinner parties. Mycelium can be used to make packaging and clothing. Fungi have been used to clean up oil spills, and an itaconic acid derived from a fungus is even used to make Lego! Fungi are also eco-warriors. They are absolutely essential to a healthy soil, and play a key role in trapping CO2 fixed by plants into the soil, preventing its return to the atmosphere. Over a thousand billion tonnes of carbon are locked in the world's soils. That's more than twice the amount of carbon held by all the trees on Earth. If the activity of soil fungi were to increase, they could potentially solve global warming on their own! But despite their many uses, and dangers, of course fungi aren't actually 'good' or 'evil'. They are an incredibly adaptable and distinct life-form, playing a key role in terrestrial life on the planet. And for that - and not just because they taste great on pizzas - they should be celebrated.