How can an ant gauge the area of a potential new nest site to see if it is appropriate for its colony? One theory is that it uses a technique based on the probabilities of random paths crossing each other. The ant will wander around the site at random, leaving a scent (orange). The ant will then come back later and do the same thing (blue). The number of crossings that it detects in the two paths is roughly inversely proportional to the total area of the new site. Here the maths of probability is providing a rough-and-ready way to approximate an area, simple enough to be programmed into an ants behaviour. [more]