What are these bugs on my porch and how can I get rid of them? They latch onto the siding upside-down or sideways and stay there for weeks. I've never seen them move. I noticed they had moved position after it rained heavily. Can I just brush them off?
From your pictures, those look like discarded cicada husks. They're not "alive". You can just knock them off with whatever tool you prefer for such things (broom, paint scraper, etc.)
There is no real need to prevent them. The cicadas molt and move on, leaving the husks.
Those are Cicadas, they live in the ground for years and crawl out only to moult their skins as adults and mate.
They have an obnoxiously loud mating call, I'm sure you've heard it, they'll often emerge from the ground all at once, there are some places where they come out like clockwork every five years, thousands of them all in the same night, those skins can be found in piles around the base of trees, and stuck all the way up and along every branch.
What you're looking at is the empty shell, the bug has since flown away and crashed into a wall somewhere and most likely been eaten by a rodent or bird. Cicadas are dumb, they will pretty much walk inside the mouth of a predator. It's a feast for many creatures when they come out, because they are the easiest prey in the world, and they're big and juicy. There are even some cultures that cook them up for dinner. Or just pick them off the trees and munch on them for a snack. I myself have never been brave enough...