Every time i try to kill Spaw, no matter if i do the final blow, or leave it for Glut himself ... the next turn he is hostile, aswell as whole colony. :-/
Even tho such twist fits his nature, i belive its a bug.

//Edit:
Update! If you turn against Glut, Spaw will become hostile too. O_o
Now im certain this DEFINIETLY is a bug.
