So still working on this species and might add a more female version too tho there won't be much difference.
But for now (might be edited or changed later):

Idk if I keep all stages or just the last (love me some shiny armor).

Their diet includes anything mineral based, which also leads to a physical change.
Image shows an example of a specimen which consumed enough metal during its lifetime to gain this nice n shiny look.

A specimen which got less lucky to consume enough minerals before it reached its maturity might stay in the first stage.

Yeah thats it for now lawl :D Idk how it gonna turn out in the end.