Overview: Watching the fascinating display of leafcutter ants at the Natural History Museum in London is one of my favourite ways to while away a few hours, but David Attenborough is operating on a much grander scale here in the last in the series. In Argentina he observes some cousins of the leafcutters who are part of a community so vast it spans an entire continent. It’s one of the mandible-dropping facts in a look at one of the key inventions of arthropods: colonies. From termites and honey bees to the leafcutters, it seems that if you want to get ahead, you move to the big city.