What are these tiny beige millipedes in my ficus soil?

All the ones I’ve seen are dead and laying on top of the soil, but I haven’t done much digging. Minimal contact (even visual) would be best. I used potted soil that I bought at Wal-Mart. Did they come in the bag, or did they get in from my house? Are they harmful? I mean, they don’t seem to have caused any harm yet, and it’s been a few months. Should I replace all the soil, or just scoop out the top layer of dead bodies and put new on top? Blarf.