Is butterflies a common noun

Yes, the noun butterflies is a common noun, a Word for any butterflies. The Word butterflies is a plural, common, concrete noun.

A proper noun is the name of a person, place, thing, or a title; for example:

• Thelma 'Butterfly' McQueen, actress
• Butterflies and Bumblebees (baby clothes and accessories), Inglewood, CA
• Butterflies and Friends (non-profit), Colorado Springs, CO
• 'In The Time of Butterflies' by Julia Alvarez