"out of box" aggro
ooth. hatches ... count down to extinction begins at what instar? The answer would be depending on the species with the caveat that there are no hard and fast rules to cannibalism because all mantids are cannibalistic. In my experience, Tenodera sinensis will start cannibalism very early despite being flooded with D.melanogaster. This thread mentions this species, so I am just using it as an example; however, it does seem to somewhat stand off the page with early aggression. We might infer from average hatch sizes being large at around 175 nymphs that immediate nutrition is paramount for the survival of the robust nymphs and that their intense hunger drives them to hunt early. I witness cannibalism at early L-2 with this species.
game of hunger
Not all mantis species reach satiety as easily as others; a common example is that Parasphendale sp. on average, have bigger appetites than, Phyllocrania paradoxa. Hunger can be viewed as the catalyst that spurs the drive to hunt and appetite being that which, dictates the intensity of prey drive aggression during the hunt. In a shared enclosure with the same variables, P. paradoxa would probably fall victim to Parasphendale sp. If you were to switch their appetites, I would hypothesize the opposite conclusion.
I've been "raptored" (B.mendica, Tenodera sp. Heterochaeta sp); however, never bitten. I'll be sure to log a bite report the day that happens; although, I have certain doubt that it will. The best mantis temperament for me would be one that is highly communal within species (shared parenting, etc.) and incredibly aggressive (active stalking, communal hunting) towards prey. To my knowledge, a mantis like this does not exist. That'd be pretty rad, though.
Have fun