Sometimes when the prey is too small, frogs get turned off. Usually you have to feed them a piece as long as the distance between the eyes but with nightcrawlers you can go longer than that because they do not cause impaction since they do not have an exoskeleton.

My frogs love night crawlers and eat them like spaghetti lol, but most frogs also hate red worms because of the flavor their slime produces when in distress. You can also feed hornworms and waxworms as treats so your frog can like the worm texture better.