I have a mega huge barn, and a crawl space, a dank cool always-open basement, and I have never seen a black widow in any of them. Also, I'm pretty sure they're arachnids, not insects but I'm no spider-ologist.
If I were in your shoes I'd hose the hell outta the place with some nasty deadly bug-killing crap. I'd also recommend you wear gloves messing around in any kind of out-building. Especially in the dark. Especially if you have black-widows.