If your cham ate a full cup of horn worms, with the last ones being the size of the one in your picture, he doesn't need to eat for days! I think the tendency of most keepers is to overfeed. I purposely let my chams go without food for a few days sporadically to keep them willing to eat whats on their dinner plate.
Some tricks on the HW:
1) At about 60 degrees, they slow down growth.
2) One day in the refrigerator and 2-3 out will also slow them down. Don't refrigerate them past one day, or they may die, depending on your refrigerator temperature.
3)
Great Lakes Horn Worm's food is better than others; It doesn't give the cham the dark staining fecals that other foods do.
4) Problem with breeding is, you can't keep the eggs dormant by putting them in the refrigerator, once they are fertilized and laid it is "Go Time!"
5) Haven't tried this one, and nutritional value is questionable, but others have fed them carrots when they run out of the HW chow. Maybe it slows the growth? Wouldn't recommend this from a nutritional standpoint.
6) You can hatch the moth and feed it off, pretty big though.
Cheers!!!
Nick