Some things are best done with friends, but when you have no ears and eyes, it is hard to know when your friends are around to help you. Bacteria have solved this problem through a process called quorum sensing. Bacteria produce molecules called autoinducers (AIs), and they also monitor the number of these AIs in the environment. As more and more of the same type of bacteria accumulate, so do their AI’s, letting other bacteria know that they are in good company. When a critical mass is reached, the AIs can start to regulate the expression of genes that are important for group behaviour – such as bioluminescence (glowing). While bioluminescence is not worth investing in alone (no one sees one little glowing bacteria), when done as a group the effect is spectacular.