According to BUGS2 Arc, they lay eggs through asexual reproduction, copying their genetic information and rendering their offspring immune to whatever killed them. When Evolved Terraformars hatch, they are shown to be fully-grown adults. By that logic, every killed roach should spawn new Evolved Terraformar, and Shokichi Komachi would be pretty useless by Annex I Arc.
However, manga later contradicts this by having these ninja kid things running around. I'm pretty sure a Terraformar is seen walking around with its young after snapping Nanao's neck in the manga, too.
So, how does their life cycle work?