Do NOT scratch! It can be really easy to get those suckers infected, and boy, I do not wish that upon my worst enemy.
Along the same idea of the lacquer hair spray, clear (or any color, but how many of us want red specks all over) nail polish painted over any chigger bites will suffocate them and you will be just fine. Unfortunately I don’t know how to avoid them or keep them from congregating. Good luck!