I think the drones are such a great piece of economical storytelling because we as the reader understand two key things about the trolls - that they are social insects and that they live under a militaristic regime (both of which are also such stock staples of the sci fi fantasy genre that they take very little effort on the part of the reader to comprehend) - and just by giving these things the name “drone” we are immediately able to draw the connection to what a “drone” is both in insect social structures and in a military technology context. and from these inferences we can very easily and correctly assume basically everything there is to know about these very much minor but essential worldbuilding characters that don’t even make an in-person appearance in the story until well over 2000 pages after their introduction