Foreword: Please excuse me if some of the tags that I've attached to this question are inapplicable. I'm just trying to make sure I've covered all my bases.
According to every dictionary that I've come across, as well as all professional sources of relevance to the topic, the word "drone" in the context of a eusocial species is only properly used when referring to the fertile male caste of bees, ants, and wasps.
However, somehow the word has gained a very different meaning when it comes to fictional eusocial species, where it now serves as a presumably "cooler"/exotic-sounding synonym to what real-life biology knows as the "worker" caste, while males (if they even exist) are never referred to as "drones"; this even extends to examples where the species is obviously based on bees/ants/wasps.
How did this come to be? Might it be related to the fact that "drone" can also mean "one who performs menial or tedious work" or "drudge", i.e. "a person who works in a low servile job"? (I rarely see the word being used in this way, though; the first time I remember seeing such usage is in Sid Meier's Alpha Centauri, as a term for the working-class citizens of one's faction.)