species identification - What is this animal that hides in dustlike structure?

I'd like help identifying the species of animal in these two photos. There's some dust(or dust-like substance) with something alive inside of it (possibly a larva or I don't really know what to call it). This appeared in a couple of hours in the wall. Please, try to even just guess what this could be (I can't think of anything!). Very odd... I don't even know what tags I hsould use for this!

Thanks in advance new photo