Animals have evolved various methods of preventing predators from eating them. A fish that can change the color of its skin to blend in with its surroundings will be less likely to be killed than another fish that is unable to camouflage itself this way. However, there are no fool-proof defenses. There will always be a predator that has adapted to the protective behavior by being sharp-eyed enough, fast enough or in some other ways able to overcome a potential prey’s defenses. If this wasn’t the case then the prey species would essentially become invincible, their numbers would skyrocket and the balance of the ecosystem would be upset. This, in essence, is what happens with some animals that are introduced into an alien environment and live in an area where no predator has co-evolved, but that’s a subject for another diary.