Why No Giant Insects?

Readers my age will remember the days of staying up late to watch black and white films like Them and The Deadly Mantis. But why, in real life, are there no insects larger than small rodents? This study pinpoints the answer. The tracheal channels carrying air around the insect's body have to become proportionately larger as the creature is scaled up. The result is that the current record-holder for insect mass, the beetle Titaneus giganteus, is as large as a modern insect can get.