So one thing I was wondering about the slug genders, do you know what gender Boomslug is? Boomslug is always described as “it” in the book as far as I can tell, while the others are referred to as “he” or “she” at one point or another.
From what I can tell the characters basically guess/label the slugs as they see fit. I think FM thinks about how Spensa calls Doomslug she but it seemed to be an arbitrary call on Spensa’s part ... I don’t know how close the slugs are to real slugs, but irl slugs are actually hermaphrodites.
They are making it up.
Slug sexuality is not canon, but in my mind they are hermaphroditic, like banana slugs.
Which means they would all be both genders, technically.
Boomslug is tagged male at some point, but I don't remember when.