As with the earlier post this question comes from the handwritten questions people leave for our featured Scientist on the Spot. Not all the questions fall into the given scientist’s area of expertise, but are still good questions, so I’m taking a stab at answering them.
This question is particularly timely: “How many days does it take for a Monarch butterfly to hatch?” Timely not only because the migration of Monarchs to Mexico begins in August, but also timely for me on a personal level as one of my favorite places to visit with my mom, wife and daughter at the upcoming Minnesota State Fair is the butterfly tent! (Which, devoted fairgoers, has moved to east of the grandstand on the corner of Dan Patch Avenue and Underwood Street.)
I am assuming the question is really how long it takes the butterfly to metamorphize from a caterpillar to a butterfly. I ask because the caterpillars themselves hatch from eggs. The whole process, from egg to butterfly, takes four weeks. The eggs hatch after 7-10 days, and the process of hatching from the chrysalis takes around two weeks. The length of these stages is impacted by the temperature – the cooler it is the longer this process takes.
Now, here is one of the really cool things about Monarchs, I think. Each adult butterfly lives about 4-5 weeks. But once a year in the autumn there is a "Methuselah generation" which will live 7-8 months – effectively outliving the combined lifespan of their parents, grandparents, great-grandparents, and great-great-grandparents. It is this generation of butterflies that migrates from Canada and the United States to either Mexico (if they are east of the Rocky Mountains) or to the Southern California cost (if they are west of the Rocky Mountains – though this population seems to be shrinking – see an earlier post on this).
It is incredible to me that these insects can make a migration that they have never made before, that their parents never made, their grand parents never made, as well as their great-grandparents, and great-great-grandparents. Bryan wrote a post on some recent research that butterflies, “sych UV information up with a natural clock in their brain. By combining these two bits of information, monarchs are able to determine the angle of the sun and always head due south,” which I think is really amazing.
Thanks for the great question!