Pillbugs! They are also known as pill bugs. Or roly polies.

Not sure if they are the reason the moss isn't 'sticking' into the dirt.

I used to think they were eating all my moss too, but I'm not so sure now. I think they like to dine on dead vegetation, and it could be that the moss was dying anyhow. I think it's more likely the soil isn't acidic enough for the moss and it's just not happy.

The area I planted my moss in is shady, usually moist (and boggy when it rains), has poor drainage, and most everything else died or did poorly. I packed down the soil really hard, and added a little soil acidifier for good measure.

Below is a picture taken a few months after I planted it:

{{gwi:599852}}

Here is a link that might be useful: Deborah's Garden