Harvesting blood worms for aquarium feeding

Is there much of a danger from getting bloodworms from old standing
water in buckets left outside, and feeding these to fish in an
aquarium? I'm unsure if there is a high potential of disease transfer
or some other risk I may not know about. Any advice would be
appreciated. Well, most any advice. I'd like something better than
"If you are in any doubt, then you should not do it."

Thanks
Ron