Beware: Parsing
Of course, because the ankheg automatically deals damage on its turn when it makes a grapple check to hold, the damage must be done on the ankheg's, and never the fighter's, turn.
[/Parsing]
How does that logic fit you?
If the creature does not constrict, each successful grapple check it makes during successive rounds automatically deals the damage indicated for the attack that established the hold.
Although you could argue the importance of the word "successive". You might say that this word implies that damage through grapple checks may only be inflicted once per round, on one particular initiative. Because the fighter and the ankheg both go in one round, the damage is done during one or the other.Wippit Guud
If that's the way it goes, Improved grapple is sick. If someone tries to break free, and fails, he takes damage for it.
Of course, because the ankheg automatically deals damage on its turn when it makes a grapple check to hold, the damage must be done on the ankheg's, and never the fighter's, turn.
[/Parsing]
How does that logic fit you?