We spotted this thing crawling around a (thankfully empty) bowl in our apartment in Barcelona, Spain. I have never seen anything like it. It appears to be some kind of caterpillar-like insect, but it is inside a flat, leaf-like shell. It can only move by sticking its head out a hole in the tip of the shell and it has to pull itself by its front legs (no legs under the shell). But it can actually pop out of either end of the shell! When it's threatened, it just hides inside the shell completely.
I'm completely flummoxed as to what this thing is. Does anyone have any clue?
(click the images for full-size)