That Butterfly Bush's bloomed form has fully formed wings, along with Lavender. I wonder if Pests=Fully evolved FKG might be a thing. Thus the reason for the never ending pests.
For the record, Edelweiss CSQ equipment:
Precious Memories Earrings 245/36 (green)
Nutaku ID: 556500612
I thought they came from dimension-hopping reality warpers.
I think both of the latter are right: ordinary arthropods and invertebrates were corrupted by reality-warping dimension-hopping beings that at one point were referred to as demons (I don't know if that's for lack of a better word, or because this was really long ago and historical memory is mixed with superstition, or they really were demons).
It would be a nice twist though.... (one that the Puella Magi series and i'm sure a few others have done).
Pests actually turning out to be corrupted Flower Knights.... turns out what you were fighting is what you can become...