When walking along gravel roads running through the jungle you'll often find successive columns of leafcutter ants, like these. Next to humans, they form the largest and most complex animal societies on Earth. Their nests can grow 250 feet in width, and contain up to 10 million individuals. The ants use the leaf cuttings to cultivate a fungus garden that they both live in and use for food. They can strip a whole tree down in 24 hours.