Monarch butterflies have four or five generations and the last one is migratory. This generation is unable to survive the harsh winters of North America. Each autumn after stored the energy reserves required, begins a long journey of over 4000km, from Canada to the mountain ranges of Mexico. When spring arrives, the Monarchs head north and mate. The migratory generations live about seven months (because they remain inactive in winter) while during spring and summer, when the Monarchs are sexually active, the lifespan is only two to six weeks.