When running out of net cage, i sometimes put 200 mantis together in that foot cube cages. and remember once i had 300 orchid mantis hatchling in the same cage as they all hatched at the same time.
I assumed you have P. ocellata right now, they preferred not to eat each other when plenty of fruit flies are available. You can increase the surface area within the foot cube net cage with plenty of branches and leaves, i like to coil up some raffia on the fake branches/leaves too to further increase moulting surface and provide more hiding spots as well. But for the food, i prefer to use flyable fruit flies (wild) instead of wingless/flightless fly when keeping them in a large cage. The wild fruit flies will fly around and cover a larger area and thus giving better chance for the nymphs to catch/eat. Wingless/flightless fruit flies prefer to stay still at the bottom or at the highesit point and remain still, unless you shake the net cage and trigger the flies to move again, so without any movement to trigger the nymphs to catch the fruit flies they might turn on to each other when starved. Regardless, cannibalism is all possible with you keep bunch of them together, but with 80 nymphs you can afford to lose some, but proper way of feeding and setting can certainly reduce casualty.
