Weird bugs

Just before moving into this current apartment, I was finding these weird little bugs in what would be my bathroom, which was then empty. At first sight, they looked like little pieces of wood chips or pulp, but I noticed they'd start to move slowly in a rather shakey, jagged sort of way. And then, on closer inspection, I noticed a little black 'head' that would poke out at one end.

They looked harmless, so I nudged one a little bit and it naturally pulled its 'head' back into what I figured was a shell of sorts (the woody looking part). To my utter amazement, the 'head' popped out the other end after some time! It proceeded to move about as normal.

I finally managed to get a decent photo of them when I found two in the kitchen last week:


I patiently waited till one of them have emerged quite a bit from the 'shell', such that I could see its legs, before taking this photo. I never saw it emerge completely though, not that it would have I suspect. I left the kitchen after taking this photo, and when I returned an hour later, they were nowhere in sight, so they move a lot faster than I thought. They're pretty small too - the entire 'shell' is only about 1 cm in length. Here's a close-up of the not-so-shy bug:


I've been trying to figure out what the heck this bug is, but haven't found anything remotely similar to these. I almost think that they use materials from their surroundings to build a shell that they can move about inside.

Anyone knows what they are? Do tell me! It's very intriguing!

*Update*

Finally, the mystery solved! Someone identified the buggers for me at Yahoo Answers: they're the larvae of a case-bearing moth. See more info here:
http://edis.ifas.ufl.edu/pdffiles/IN/IN12900.pdf