I don't know what a "global AI script" is,but is sounds fun :D.
*facepalms*
In long terms it is:"global Artificial Intelligence script"
(hehe, wrote that good in one time, i couldn't believe that :P)
But that script will determine how the bugs will act in situations.
How they will walk,talk and crouch their way to the player (lol, i guess they don't talk xD).
Because this isn't like standard included with the models themselves ;)
Hoping you understand it now..