Let's say that in a fictional world (the world of Heroes of Might and Magic IV in my case) the square-cubic problem of insect respiration is somehow solved, so I have giant mantes roaming the area, and used in enemy ranks (let's say, they are controlled by magic). It is hard to judge the exact size (as miniatures on the battlefield are not as different from each other as some art shows), but the mantes are at least as large as a horse a typical humanoid could ride, and could be as big as the mighty Black Dragon in this HoMM III intro.
I ask this question because I remember trying to kill or otherwise harm insects in my childhood, and they were by no means really fragile! Yes, if you throw it into a fire, it will burn, but I can't imagine any other way to kill a mantis except from evoking a fire big and hot enough. Chitin is very resistant to being cut, smashed, etc. Moreover, insects are dumb, and as far as I know, they don't feel pain at all, so even if it loses a limb, it is not stopped.
Is there any way to quickly dispatch a giant mantis without resorting to fire?