You might want to use a light to keep the worms in this thing.
And buy a copy of "Worms Eat My Garbage", which will save you a lot of trouble.

@steamyb..

thanks. the light is a good idea. the containers are outside on a second story balcony. i was more concerned they would drown in the water reservoir.

i already have at least one worm in one container. i just picked it up off the sidewalk and dropped it into the container about two years ago. while planting in the box last year i came across a single plump, vigorus worm but i don't think it was the same one i dropped in. i don't know if there are more in the box or not. i was really surprised that they did not all crawl through the screen and drown.

i had a suspicion they would not but with 250 competing for space i don't know.

i will look into the book too.

also, if they start escaping i can plug the overflow hole with a .25in test-tube stopper.