Ashtagon
Adventurer
I'm not sure a fly has any organs capable of anything even approaching a verbal component.
It not only lacks a mouth/tongue/jaws capable of human speech and language, but it doesn't even have a voice box (insects have a method of getting oxygen that doesn't actually involve anything analogous to a lung).
So, they can cast any spell that requires only somatic components. Material components will be tricky with no hands or manipulative limbs, and with no voice, verbal components are out too.
It not only lacks a mouth/tongue/jaws capable of human speech and language, but it doesn't even have a voice box (insects have a method of getting oxygen that doesn't actually involve anything analogous to a lung).
So, they can cast any spell that requires only somatic components. Material components will be tricky with no hands or manipulative limbs, and with no voice, verbal components are out too.