Goldfish will pretty much eat anything.
If you do not use pesticides, you can try them.
The best 'wild caught' food I give my Betta's is mosquito larva.
That's what blood worms really are (read your fish food label)
Clean clear water left outside, a fine net to get the larva, feed as much as your fish will eat in 5 minutes. Don't leave any alive in there or you will get mosquito's in your home!
You can freeze them, stock up for winter!

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