It’s weird that I’m the opposite. Spiders of any size have absolutely no effect on me. But snakes trigger some sort of innate response. I wonder if it’s tied to geographic origins of our ancestors?

I'd guess it's due to some kind of imprinting during childhood, similar to taste. The widespread prevalence of irrational phobias and methods for curing them certainly suggest to my untrained eye a learned behavior rather than innate.

I have no idea. I do not fear any of them, but I would fear some in real life were they near me, but only because I know they might be able to kill me.

Cockroaches are just, like someone else said, disgusting to me, especially if they are at home. If they are outside I could not be bothered.