Thank you for your replies. I'm gathering that the larva builds this to metamorph into the adult moth stage, am I correct? If I collect a leaf and put it in a jar, can I expect to see a moth emege? If so, when? Is there a way to know if the moth has already emerged w/o opening the case?

The bag is a multi-purpose structure. Shortly after hatching from the egg, each larva begins construction of its own bag. As the larva grows, so does the bag, with new material being added regularly.

Toward the end of the final instar, the larva finds a vertical surface to which it attaches the bag. The larva molts a final time and pupates within the bag. It is this phase with which most people are familiar, as houses are a common vertical surface.

The adult moths eclose (emerge from pupation). The males take wing in search of mates; the wingless females remain in their bags and attract mates via pheromones. The males mate with the bagged females.

The females lay eggs within their bags and die; the eggs overwinter in mom's bag and the cycle begins anew next season.

Hopefully this answers your questions, or at least is as clear as mud.;^)

Just 2 questions:
1. Does this mean they carry this stick bag around with them until they attach it and for how long?
2. Does this mean there is always something in the bag at any given time?
I would LOVE to see this under construction.

I've put one attached to a leaf in a jar...can I expect something to come out of it?

1. The larvae carry their bags around with them their whole lives--several months.
2. The bag may contain eggs, a larva, a pupa, or an adult female. It could stay attached indefinitely after the hatchlings (or adult male) emerge, in which case it would be empty.

I collected one of these once, and what emerged was a number of tiny larvae, already wearing tiny versions of their mother's bag. You could also get an adult male:

If a male emerged you would see the pupal skin sticking out the top, I think.