I found a spider in the garage a few weeks ago... I kill some every so often but this has been the first black widow I found. One of my neighbor said he had plenty when he first moved in.
I don't like it so I decided to "seal" the garage. I ordered better bottom seal and also got the sides. Here in Texas they always cut at 45 degree the side frame that touches the ground. That leaves an 1"-1/4" (triangle) gap

I never really understood why they are doing that. I patched it with concrete.
That will also stop the mice. Killed a few last fall.
Next week I will seal the gap between the concrete floor and the framing with polyurethane caulking. They only had the seals in white so I'll have to paint them later.
I got the aluminum rail (L-Shape) and added a 1/4" foam inside. Worked great, it cushions better and closes all the gap that I was seeing before with the old rubber.
I already have seen an improvement. A lot less bugs, actually none (could also be the cold weather). It will never be 100% but it's 20 times better then what it was.