Crypsis works by making an animal impossible to see. Aposematism works by making it impossible to miss. Both are anti-predator adaptations. How can advertising yourself to predators be a defence at all?

A. Because aposematism is only viable alongside a real defence.

A toxic caterpillar gains nothing from the predator that eats it; it gains from every other predator that ate one before and learned. Conspicuousness is what makes the lesson generalise, so the strategy trades individual concealment for population-level protection, and needs a real defence, a memorable signal and predators that learn, all at once.