Several years ago, I noticed a number of these odd structures dotted about the forest where I habitually photographed bugs. They consisted of short segments of plant stem, cemented (?) together and glued nearly perpendicular to the surface of leaves. I don't remember what kinds of plants they were on. Anyway, one time my curiousity got the better of me and I ripped one open to reveal a worm-shaped.. what, larva? Pupa?
Anyone have any ideas what creature is responsible?

I also once captured a small beetle crawing on one - but this might be coincidence.