Answer:
Option A
Step-by-step explanation:
Why?
Well to start of Option B is way too specific. Unless you are only going to talk about why ants play critical role by aerating our soil then use this. But Option A is better because Option B could be a Detail why ants are important. Remember how a paragraph is written.
Opening Sentence, usually 2 details and 2 examples but can be more and a Closing Sentence.
What I'm trying to say is that Option B is a little too specific and giving a little more then a thesis should. But you could choose either. They both a good thesis.
Answer/Opinion: Option B