Night Crawlers are an excellent food for frogs and are very nutritious. They make an excellent staple. They are also good because they keep the frog's feces soft so impaction is not a worry when feeding them to your frog.
Thank you Grif! Bert seems to really love his crawlers and he poops regularly. I even caught him eating his shed...twice! Now that I "think" he's regular, I'm gonna grab some dubias for treats.