Yay! I had to go on a trip that took two days. When I came back, I found a snake skin. The smaller garter, the one that wasn't eating, had shed while I was gone. I stuck in a worm and he ate it!
It seems that the larger snake is about to shed. He was settled in a container filled with damp paper towels and his eyes were a blue-ish color. Compared to the smaller garter, the larger one seems really dull and pale.