Isidore of Seville [7th century CE] (Etymologies, Book 12, 8:8): Butterflies (papilio) are small flying creatures that are very abundant when mallows bloom, and they cause small worms to be generated from their own dung. - [Barney, Lewis, et. al. translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Worms 9.32): Butterflies, as the Liber rerum says, are flying worms which mainly rely on flowers and take food from them. They copulate after August, and the male dies after copulation, while the female lays the eggs; after having laid them, she dies. The eggs last through the winter and in the summer season produce worms, which, strengthened by the heat of the sun and the dew of the night, grow wings and fly away. - [Badke translation/paraphrase]

Bartholomaeus Anglicus [13th century CE] (Liber de proprietatibus rerum, Book18.46): ...for hée [caterpillar] taketh thin wings and broade, and flyeth up hether and thether fréely in the aire, & as many coulours as he had first in the body, so many diversities he sheweth in privie winges, and such a flieng worme is called Papilio. And Isidore sayth, libro 12. Papiliones bée called small Fowles, and bée most in fruit, as apples, and bréedeth therein Wormes that come of their stinking filth, as Isidore sayeth. For of Malshrags] commeth and bréedeth Butterflyes, and of the durt of Butterflyes left uppon leaves bréedeth & commeth againe Malshrgges, & doth lesse harme in gnawing & fretting when he flyeth, then when he créepeth. And Papias sayth, that Butterflyes bée small flyeng Flyes, that come by night when lyght is kindeled in Candles, and labour to quench the lyght of the Candles, and so they be burnt in the fire of the candles, & sometime when they labor to destroy light of other beasts, they are punished and hurt in their own bodyes. - [Batman]