How Many Monarchs in This Forty-acre Field? These pictures were taken in late August in an alfalfa field in Minnesota. The field was in full bloom and it was full of monarch butterflies. There was one butterfly every 8 feet! The field itself appeared to be fluttering. How many monarchs do you think were nectaring in this single 40-acre alfalfa field? Try yourself, then see what we think >>. This Season Teachers Kids Orientation Registration Search Copyright 1997-2009 Journey North. All Rights Reserved. Questions or comments? Contact us.