Like Bryce said, if the worm is too long, just cut it in half. Now you have 2 worms!
And I can say from experience that red wigglers are no good. I don't know why pet stores bother carrying them, some kind of critter must enjoy them. But I tried feeding them to one of my toads, and she hated it, and actually ran away and hidwhenever she would see one after that!
Earthworms / nightcrawlers are great though. The 2 toads I currently have love them.