oooh that sounds mean but effective!!
I left the mothball one more night, this morning they were still moving like little bug slugs. Have taken the mothball out now. Experiment is over!
Barrie, I can recommend using the ball when the lid is off to get the bugs moving and up the sides of the container so you can wipe them out with a cloth. I also suspect that using mothballs in the box might prevent the bugs coming in the first place. Since I don't have anywhere to keep the worms warm but not fill my house with vapours I probably won't get to test this theory at least till summer.
If anyone else has any experience with using mothballs, I'd like to hear about it.
thanks