I was just thinking today that I remember hearing that some insects like ladybugs and monarch butterflies are poisonous to birds that eat them. I got around to wondering how such a trait could evolve. The thing is that, while I see how being poisonous is advantageous to ladybugs in general, I don't see how it helps poisonous ladybugs over non-poisonous ones. The way I'm thinking of it, you had all these pre-ladybugs crawling around that were not poisonous, and then one comes along that is poisonous. How does that help him? If he does not get eaten before having children, then the poison did nothing for him since it only hurts birds that eat him. If a bird does eat him before he has children then the bird will learn not to eat any ladybugs, but the game over for the poisonous bug, and we have to wait for another one to come along before ladybugs can become poisonous. I thought of a few things that might solve the problem, but I'm not sure if they're true. For instance if the trait of being poisonous arose simultaneously with the trait of being brightly colored then birds would learn not to eat brightly colored bugs by eating a poisonous bug. This would mean that if the original poisonous bug happened to pass this trait on to a sizable number of other bugs before being eaten, then a few of them could be eaten and this would give an advantage to the rest. Another idea would be that the bird can somehow tell that a bug is going to taste bad by smelling it or something. Or maybee there is something I am misunderstanding about the way all of this works: I am relying on my memory of this and I don't recall the source. Any ideas?