When T. rugatulus [ant] colonies in coniferous forests choose a potential nest, they dispatch about 200 scouts to scope out the territory. If a scout thinks a nest will make a good home, it releases a chemical signal that attracts a single colony member. If the recruit likes [a la Facebook? -- JB] the site, it also will release a chemical signal and repeat the process.--Melissa Pandika, "Ants make tough choices better when working in groups, study says," Los Angeles Times
The number of recruits then steadily rises until it passes a threshold, or quorum. That’s “when things really take off,” and the recruits carry the other ants piggyback to the site, said ... Stephen Pratt, a behavioral ecologist at Arizona State University.
Image from article, with caption: Scientists have found that Temnothorax rugatulus ant colonies could consider two competing nesting sites and choose the better option if the difference between the two options was small. But when the difference between the nests was obvious, colonies were more likely to choose the inferior site.