I was watching a nature program on PBS and it was observed that poisonous snakes and other poisonous animals tend to be brightly colored. This raises an interesting explanatory question: why make yourself so conspicuous, both to predators and prey? The suggestion made was that some kind of altruism is at work–kindly signaling to others that you are a dangerous character best avoided. But animals don’t engage in this kind of altruism, so why do they signal their presence so rashly? I think the reason is to deter other animals from ganging up on them: it warns other animals to keep away from them, not for their sake, but for the sake of the snake. But why, if the poison is so dangerous a weapon? Because the poison is very limited in supply: the snake cannot kill or incapacitate one attacker after another, because its poison will quickly run out. If a gang forms against it, it will eventually exhaust its arsenal of poison and then become vulnerable to attack. So it tells other animals that it is poisonous and dangerous, as if daring them to attack it. It’s a form of bluster to deter the collective attack: “Don’t even think about it!” But in fact the snake is very vulnerable to group aggression–unlike, say, the lion, which can bite over and over again. Poison is a one-off form of defense. Bright coloring is, for snakes, a complex form of arms-war trade-off.