For one, black soldier fly grubs contain about 30-50x more calcium than mealworms. Chickens can consume more calcium from a handful of BSFL grubs than they would with 2-3 pounds of mealworms. Calcium is a very important nutrient for birds, especially during nesting season.
Additonally, this is spot on and true.Once feed the chickens with mealworms the mealworms will actually cause a calcium deficiency to happen, because they have a negative amount of calcium. (Hard to explain). All of the hens started laying soft shelled eggs as a result. But immediately switch them to the black soldiers fly larva, and also added eggshells to chicken's diet in a separate bowl from the oyster shell. It was 2-3 days until started seeing healthy strong shelled eggs again. There really is a serious difference betwen mealworms and black soldier fly grubs.