Other mistake: Wouldn't flying out of the water with the unconscious Z in his arms be kind of tricky for Cutter, as his wings would be soaked?
Factual error: Even if he was falling hard, Mandible still would've survived hitting the overturned root, as ants do not have much body mass.
Answer: It seems there are cases where smaller ants are soldiers, and larger ones are workers. Remember the workers didn't seem to care that Weaver was huge and muscular.