Sorry, but that seems very cruel. Why not just release them after hatching so they do not eat each other? As for my experience with mantids, I have never brought the eggs in to hatch, but I recently notice several small ones hanging out on my deck and porch. I also came across an adult of which is the first of it's species I have seen in the area. I am use to seeing Large florida mantis and Carolina Mantis, but the one I recently came across was quite large and colorful. It had blue wings and was trying to blend in (rather successfully) with the butterfly flowers in my yard.