The babies will most likely respond to the flies quicker. Crix are bottom dwelling and hide. The flies move fast and all overthe place. This will illicit a feeding response from the hatchlings. They will feed more and days faster with flies. I have tried to use crix only, sometimes with no success. The same day, i drop in the flies and the buffet begins. Plus, the smaller the prey, the easier it is digested. Therefore, promoting faster growth thru better digestion and more food. If you do go crix or roach only, you may have to use one fly culture to entice them to start eating. Trust me i hate using the flies. But even at two months old, they just rip thru the flies, even after filling up on crix. I think of the flies as spackling or mortar. They fill in the voids of the tummy.