<P> By the end of October, the population of monarchs east of the Rocky Mountains migrates to the sanctuaries of the Mariposa Monarca Biosphere Reserve within the Trans - Mexican Volcanic Belt pine - oak forests in the Mexican states of Michoacán and México . They also overwinter in areas that are privately owned . Some monarchs migrate to other locations such as Cuba and Florida in the fall . Two migratory fly ways exist through North America . One in the Central states leads to the Mexican overwintering areas and a smaller flyway along the eastern North American seaboard . The timing of the eastern flyway lags behind the more central flyway . Monarchs migrating along the coast are less likely of being recovered in Mexico . This suggests that butterflies migrating along the eastern seaboard are migrating to locations other than Mexico, or they have a higher rate of mortality than those migrating inland . </P> <P> Monarchs respond to different cues that promote the fall season, southern migration . These include the angle of light coming from the sun, the senescence of larval host plants, the decreasing day period and temperature drop . The migration begins at the northernmost summer range approximately in August . Migrating monarchs are thought to rely heavily on the nectar of fall flower composites that lie along the migration path . </P> <P> In most individual adult butterflies, diapause begins with the its southern migration, but unlike other insects in this state, it remains active . When diapause is initiated the butterflies accumulate and store lipids, proteins and carbohydrates . Monarchs migrating to Mexico accumulate more lipids than those migrating to California . Fats and lipids reduce water to provide energy reserves and prevent desiccation . These substances are used to maintain the insect throughout diapause and to provide fuel for development following diapause termination . It occurs genetically well in advance of environmental stress . It is a state resulting in the cessation of high - metabolic activities including reduced oxygen use . </P> <P> Monarchs in diapause of the fall migrating population are physiologically distinct from those in active reproduction behavior in the spring and summer . In diapause, the measurement of fats and lipids levels a can be as high as 34% . The fat storage organ is substantially larger in migrating and overwintering monarchs compared to the summer generations . Samples of tissue excluding the fat body also show higher levels of free lipids in the hemolymph . Females in diapause show little evidence of mature eggs . Mating is repressed and only occasionally observed among overwintering monarchs . This is thought to increase the survivability of winter populations and maintain fat reserves that will promote spring northward migration . At one site, the population stayed in diapause until the middle to the end of January . By the beginning of February the day length increases to just over 11 hours, the point at which monarchs come out of diapause . </P>

Where do monarch butterflies go in the summer