Changelings are eusocial pseudo-insects with 3 distinct life stages and 2 distinct sociobiological roles.
 
They start their lives upon hatching as black and white larva with blue compound eyes. Then after reaching a certain weight, they pupate in a cocoon and emerge as colorful subadults about the size of a pony toddler. After about 20 molts they reach their adult size. Though there is lots of color and body variation among changelings, there only appears to be two biological roles, queen and worker. The role of queen seems to be acquired by the most authoritative worker in a given queenless group, or by deposing the old queen (like Thorax did). This means Changelings are sorta both a clownfish AND honeybee scenario, in terms of sex determination. Drones are never mentioned, so I’m assuming they either don’t exist and Changelings are a single sex clonal society (where only queens have active reproductive systems), or drones are short lived and fly off to neighboring hives to mate shortly after pupation. Drones could possibly exist within the hive and function as workers, but for mating they would still need to fly out and visit other hives to prevent inbreeding.
 
Changeling diet is mostly energy based, and they evolved mimicry to feed off the extremely magically energetic pony races. Normally the process is pretty benign, since ponies produce way more magic than their bodies actually need. A regular Changeling can survive off of regular social contact with ponies and other Changelings, with the occasional realmeal thrown in.
 
Buuuuut, Changelings can’t live a healthy life off pure energy… they need physical food to supplement their diet. Queen Chrysalis was convinced this wasn’t true, and forced her whole brood onto the same terrible diet as her. And like her, they never matured right during pupation… they retained their neotenic grubby features and had horribly malformed legs and wings. Their constant hunger left them aggressive and desperate creatures. They only had the energy to fully mature after deposing Chrysalis and sharing magical energy among their hive-mates as they would in normal circumstances… MAGIC being FRIENDSHIP and all, positive social connection amplified the stored energy.
 
I’m sure as the franchise progresses it’ll come back and blat me in the face on these theories, but I’m not a fortune teller and TSU isn’t strictly canon so (jazz hands) eusocial bug gender/sex system weirdness!