I live in the middle of Chicago, in the city itself and in a very dense and urban part of it, and we had fireflies all summer. I'm guessing as an adult you're not out much during the hours they're out, or at least not in backyards and alleys where they tend to congregate.

They do seem fewer to me, but who knows, I'm comparing my memories to a kid's from decades ago. I wonder if anyone keeps track of this stuff. I did notice less bumblebees this year, in fact I don't think I saw a single one, but that's my own experiences and not anything scientific of course. Miss those chonky little guys.

I live in a decently rural area. This summer had a lot, for some reason, but overall I can't remember seeing many in recent summers. Same with earthworms coming out after a rain

I'm assuming you're in North America, many earthworm species there are invasive: https://en.wikipedia.org/wiki/Earthworms_as_invasive_species