Okay, my reasoning for being against the raising of follower races from normal animals.
1) New Gods OF MANKIND, not New Gods of Ecology. Mind you, it's great to know that players have incentive to care about the natural world around them, but I disagree with a game where the god of Locusts and Tsetse Flies is automatically the most powerful.
2) If it were that easy to gain a loyal following of devout worshippers, those niches would already be taken.
3) Take a look at Australia. Whenever one species becomes dominant, the ecology suffers. Basic ecology - cull the herd or it'll cull itself.
4) Of course the game is about miracles, but there are also limits. Divine Sight, for example, won't reveal such a plant until it causes problems for the populace, at which point it COULD be self-replicating.
5) I had other points, but I'm beginning to calm down now...