Aggression between members of the same species serves to secure resources, but the costs can quickly outweigh benefits. Hence, for aggression to be evolutionarily adaptive, animals must decide when best to flee, rather than fight. How its done, is arguably best understood in crickets. These insects implement the decision by simply modulating the behavioural threshold to flee. This threshold is raised by potentially rewarding experiences (e. g. resource possession), via the amine octopamine, so that the animal is less prone to flee and persists longer in fighting. Conversely, the threshold is lowered by nitric oxide, released in response to aversive stimuli (e. g. the opponent’s agonistic signals), thus increasing the tendency to flee. A cricket then flees, when the sum of its opponent’s actions exceeds the threshold. Subsequently, serotonin keeps the threshold low, so that losers remain submissive; possibly by inhibiting dopamine, which is necessary for recovery of aggression in losers.