Things start pouring out of the vents. Things with exoskeletons and acid blood. Upon entry to the room, they lunge at the two and then quickly curl up and die because of the nerve gas, twitching.

...But then they start adapting. The criminals that have taken over this world aren't lacking in creativity. The last of the insect monsters die and then crystalline monsters start following after them - silicon-based lifeforms, lacking the ability to be affected by neurotoxins. These massive crystalline insect-like beings start swarming towards them over the bodies of the dead bug-aliens.