The Limits of Insect Enlargement

If an ant, or a mantis, were to be magically scaled up to the size of a human, it would end up dying very quickly of its own accord, well before it could be a real threat (as would happen to Antman for similar reasons). An insect’s respiratory and circulatory systems, as well as thermoregulation, would not, all environmental conditions being equal, allow it to survive long by growing beyond certain sizes, much less act hostile.

In an oxygen-saturated environment, such as two hundred million years ago, an insect could grow to a size unthinkable today.

But the body structure and biomechanics of mantises and ants, as of many other modern insects, would be deleterious beyond certain sizes. Indeed, even the ant’s strength, which can lift X times its body mass, would not scale with size because it would depend on the cross-sectional area of its muscles, while its mass depends on volume.

By this I mean that its body mass would grow much faster than the strength of the ant scaled, so even it would not be able to hold itself up mechanically, beyond the lack of oxygen.

Otherwise, an imaginary hypothetical animal resembling mantids or ants, with their size-proportionate features and dedicated biology, would turn out to be more or less like the aliens in Starship Troopers.