Blast, that type of device works.

One modification I used as a kid was to enlarge the funnel hole by cutting below the screw top. The small diameter of the top limits the size of crawdads that can get inside. If you want the big boys you've got to open the hole.

Also, I dug a hole to bury most of the bottle, then piled rocks up around it to make it easier for them to climb inside.

One thing we discovered is that crawdads can't really swim up -- meaning that you don't really need a funnel to keep them if the trap is small and tall. If the trap is on its side the funnel is mandatory -- but if it's standing up the funnel won't be needed.

The trap works in cloudy/deep water. And it works without supervision -- a much better survival technique because it gives time to do other things. Multiple traps increases the size of supper.

Fishing also works well. But it has to be done by hand and by sight. Meaning it's time consuming. But if you don't have something to transform into a trap, fishing might be the only method that a person in a survival situation can use.

While the trap requires meat of some sort for bait, fishing for crawdads does not. Any bright tidbit of cloth tied to strip can entice a crawdad to pinch. But bait works better.

Regarding a folding trap, I guess any box will work -- a plastic one of some sort. Because the crawdads can't swim up, as long as the box is tall and skinny, it should work as a trap.

Sounds like something to add to the spring experiment list.