Technically they would be able to parasitize sentient creatures but because of the way they are built it is not a reliable food source on a mass scale. I imagine they were kind of forced into this ideology by their frail body structure and super long proboscis that kind of gets in the way (they don't really have the core strength to do any efficient attacks with it). Their only redeeming quality is their excellent flight and dexterity. It's has been an uphill battle for them for their entire existence, and the only way for their survival is absolute unity and making no enemies. In warfare they rely on traps and siege weapons and if that fails they rely on sheer numbers, coupled with the fact they make their homes on cliff faces, they are usually not attacked by other races. Please tell me if you have any changes or adjustments. (: