He ate a couple at first. I started with 4 and now I think I have only two....but I have had those 2 for probably 3 months, I think in the beginning, he was mostly curious, but I haven't seen him chase the two or so that I have left. I don't think they feel frightened either, because they sit right out in the open and just let themselves bask in the "sunlight" on my driftwood for hours at a time. My betta doesn't seem phased by them at all.
They were small when I first introduced them, now they are good sized.