Tempted as I am by Bruce Ferrie's idea of the 'giant wooden moth' I suspect the answer that the bat's controllers are the weak point are what you need to focus on. To do that you need to get onto the bat. That is trickier said than done as I suspect flying aboard will get you swallowed like a tasty bug. So you need to 'teleport' aboard the bat really. Mastakos devotees with feats like Travel Anywhere Within Sight, Carry Companion, and Ignore Pleas to Stop would be handy here. Remember the first of those is 'difficult' magic in Glorantha though. Lacking Mastakos devotee's going on to a Mastakos heroquest to learn the magic might be a good option.
Ian Cooper