I think these are European Nightcrawlers... I could only find one source to suggest this though.

If they are indeed European nightcrawlers they are a species of earthworm that make for a suitable feeder for your frog. I would check with the source for a latin/scientific name of this worm or some additional common names so we can clarify to be 100% certain. I do not have personal experience with this species and would prefer to err on the side of caution until we are positive.