These translucent worms are almost certainly the larvae of Fungus Gnats and, if you look closely, you may see the adults running across the soil. They are attracted by damp conditions and their presence suggests that you have been keeping your moss too moist. They also thrive on potting soil that is high in organic matter - and on peat moss!
I have done a quick online search and, apparently, they rarely harm healthy houseplants but, given the right conditions, will breed and spread to your other plants, and even to the rest of your house.
You can control them by:
- ensuring that your plants are not over-watered; allow the potting compost to dry out a little between waterings, so that it is slightly damp to the touch, but never wet;
- spraying the soil with neem oil or an insecticide of pyrethrins.
The following articles/video should prove helpful: