Lifespans vary among butterfly species. Some live for a few months, while others may complete their life cycle in a few short weeks.  According to the U.S. Forest Service, monarch butterflies typically live between two and six weeks, except for the last generation of the year, which can live up to eight or nine months.  The black swallowtail has a very short lifespan, only living up to 10 to 12 days.