They, like the Mechanical Brain Worm and other species, possess the ability to Metalization, but unlike the brain worms and Undead who primarily engage in mechanical combat, the Insect Swarm's machinery is merely a Support.
It's used to enhance their own defensive and speed attributes, or as an additional source of long-range firepower for the Insect Swarm.
But this doesn't mean the Insect Swarm can't, like the brain worms, construct the heavy artillery equivalent to large buildings within their territory.
The Insect Swarm naturally carries some extra metal, which is originally intended as raw materials for when physical ammunition is needed or when there is a need to adapt their machinery for different tactics.
But at this moment, these metals can conveniently serve as raw materials for the Giant Cannon.
