I have an theory about something in the series.
Brittany tells Sam in plague 'These creatures have been molded by the lord to be indestructible.' My theory is that each eye colour of bug has exclusive features and defence mechanisms. The red eyes (the ones that attack PB) have a curse on them.
'Those who kill these monsters shall be struck down by the next soldiers of the Gaiaphage'
Breeze and Caine kill all the red-eyed bugs, and, surprise surprise, they are killed by the next soldier of the Gaiaphage, Gaia.
This is just my theory. Don't put this on a wiki page.