Hello Judy! A night crawler would never cause impaction in a frog. What is the worm source? What is the frog snout to vent length? From reading your post, appears you just bought the frog. Please read this care article and ensure the frog needs are met: Frog Forum - Pacman and Horned Frogs - Ceratophrys - Care and Breeding.

You can feed it a staple diet of not dyed night crawlers. If frog is over 3 in. can feed whole worm, if a juvenile can cut from pointy end same as frog's length, and if a baby mouth size. Insects should be same size as distance between frog's eyes, and gut loaded 24-48 hours with carrots, lettuce, and crushed cherios/oats. Remember to use food supplements too: http://www.frogforum.net/food-feeder...schedules.html. Good luck !