My Guess: It is goat-head season. (perfect little thorny things.) There is a place on one of my routes where I pick up 1 or 2 EVERY time I ride through there.

Kevlar belted tires help. I've seen goat-heads sticking out of my Schwalbe Big Apples (2.35s) and they didn't get through to the tube! Slime filled tubes or tubeless tires with goo are perfect for the tiny goat-head holes too. The problem with liquid sealants is that it dries out in about 2 years.