I icefish with a variety of bait and normally the juice is hardly worth the squeeze when harvesting goldenrod larvae but this year- I opened about 50 goldenrod galls yesterday and I found (3) larvae.
None of the galls had exit holes and I believe the gall will not develop without the fly- so the lights are on and no one’s home (including the guy opening them). Needless to say- the child labor I employed on picking these was less than impressed with the yield. Weird year? - get out your pocketknife and let me know.

Can't help you on what's inside. I have a bunch of these in dried flower arrangements around the house.My kids used to call the long stemmed ones " head knockers" for some obscure reason.................

I use those to hold lure on the trap line. I can get my lure up in the air away from the trap.
Never used them for fishing.

I used to use them for trap indicators. Put on through the trap chain and when you get something the indicator will be missing. It worked great for those sets that did not need to be tended every day and were hard to get to.

The galls you have that are empty probably had the gall fly larvae killed early last Summer by the larvae of a parasitoid wasp, called the crypt keeper wasp. The crypt keeper wasp lays its eggs on the galls made by gall fly, which is also a wasp. The crypt keeper wasp larvae burrow in and eat the gall fly larvae. They pupate and leave early, while the golden rod is still growing the gall, so the holes close.

When I was a kid. I used to use the galls as bobbers, if I didn't have a plastic or foam one.

Keith

FYI: Pick a few galls and leave the stem long on them and they make dandy ice/wet water fishing floats!