Gaona wasn't able to identify the species of the "multicolored" spiders, but considering that this seemed like a scaled-up version of the kind of s**t he used to pull on his little sister, it must have raised the question of whether God was in fact 12 years old.
Animals just straight falling out of the sky like hail is not unheard of, and the popular explanation for it is always that strong winds manage to pick up animals and deposit them into the atmosphere. Of course, this doesn't explain why the rain was limited exclusively to spiders. Why not toads, or chipmunks, or, you know, anything else whatsoever? God wasn't even mean enough to make spiders one of the plagues of Egypt, and he was really mad that time.
Or chocolate coins.
It's kind of unnerving that this kind of thing is going on in remote parts of the wilderness where people don't usually know about it, like some divine Manhattan Project. We can only assume that God is field-testing it before combat use on a modern city.