In this photo taken Feb. 15, 2013, Monarch butterflies are collected in a net to be tested for the ophroyocystis elektroscirrha parasite that inhibits their flight, at El Capulin reserve, near Zitacuaro, Mexico. The scientist is part of a research project conducted by the World Wildlife Fund of Mexico and the University of Georgia and University of Minnesota. (AP Photo/Marjorie Miller)
Every year, millions of monarchs migrate from the eastern United States and Canada to central Mexico, a journey of over 2,000 miles. The tiger-striped butterflies arrive in late October and early November to hibernate in fir trees until February.