In my previous RPG stuff, I've generally just f**ked with the design to a greater or lesser degree, and flatly never explained it to the players in or out of character.
Any info they can find generally has more to do with observed behavior in captivity than in a natural environment, and is purely foreshadowing/tension building rather than an attempt to define castes or subspecies.
The players can draw their own conclusions if they want to, but they'll never get hard answers from me as the GM or from in-game documents.
Because ultimately my opinion is that once something is codified and has a hard/"real" answer, you've painted yourself into a corner. It's a lot more fun for me as a storyteller and a lot more tense for the players, if they never know what's coming next. Making a very explicit set of castes or defining conditions for adaptation damage that freedom IMO.