In over 9 year I have never wormed once. Never saw a worm in droppings. Here is the thing. Everything, even you and I have a healthy balance of worms inour systems. Once you start " just in case" worming" you will always need to worm. Give your birds enough space, use a good healthy deep litter in the coops and keep runs if you have them clean and you will probably never have a worm. I have not. I should say, never have an unhealthy balance of worms.
Feed your birds pumpkin seeds or whole pumpkins, winter squashes. Natures dewormers. That is what I do. In season.