Another easy way to harvest grindal worm without dirt is to feed a piece of sandwich bread instead of baby cereal. Teresa taught me this trick and it works well. You don't even have to bother with plexiglass. Grindal worms swarm around the piece of bread in such abundance that you can just pick off pure worms with the tip of a plastic knife or a popsicle stick. Another benefit of this (at least to me) is the mold inhibiting quality of cheap sandwich bread. (I don't know what they add to retard molding but it seems to be safe for fish.) I tend to overfeed with baby cereal and used to get the bedding moldy and spoil the bedding and the culture in no time. Grindal worms have voracious appetite and devour the small chunks of sandwich bread in a day. If you are worried about nutritional balance of the worms, I suppose you can feed the worms with a small amount of quality fish food.