I do have microworms here rigth now but i have been told that walter worm is even smaller than microworms. I also have banana worms.
oh wow if walter worms are smaller, then your betta frys must be super tiny!!! I dont know the live span of walter worms, but from research vinegar eel lives up to 3 days before dying while microworms usually last for 12 hours only. So i prefer vinegar eel, so it wont dirty the tank quickly like in your case with the walter worms.