Close Quarters: 15,000 Butterflies on a Branch How Much Would 15,000 Butterflies Weigh? Thanks to Susie in Texas for sharing her monarch math! "Each branch would weigh 7.5 kilograms (16.54 lbs). Things that weigh that much are my very large cat 'Pumpkin,' and my mother's weight bag with both of her 6 lbs weights, one of her 4 lbs weights, and a book."   Search Journey North Copyright 1997-2012 Journey North. All Rights Reserved. Questions or comments? Contact us.