The best answer is IT'S NOT SAFE TO FEED YOUR KOI WITH EARTHWORMS. Why? Because earthworms may contain trach parasite and other types of parasites that are harmful or bad to your koi fishes.
In my experience, after I fed earthworms to my Koi fishes, my Koi's felt a little unwell. They scratch their body to the side of the pond and to the stones. Some of them lose their appetite and some moved slow.
To be safe, do not feed your Koi with earthworms unless if you carefully culture your own earthworms or your earthworms are safe and clean.
Some of you may feed your Koi with earthworms. If you regularly feed them with earthworms, let us know in the comment below how's your Koi doing?
- If you use toxic treatments (chemicals) having residual poisons on your backyard, earthworms on that backyard are not safe to your fish.
You may add some tips or suggestions in the comment below.