Annual Life Cycle - Generations 3 & 4
Generation 1 | Generation 2 | Generations 3 & 4
Overview
Monarchs in Generations 3 and 4 are the great- and great-great grandchildren
of the overwintering monarchs. They are laid throughout the northern part
of the range of eastern migratory monarchs from late May through July (Generation
3), and late June through August (Generation 4). Those in Generation 3
do not undergo reproductive diapause or migrate, but members of Generation
4 that emerge late in August will undergo diapause and migrate to Mexico.
Life Cycle Summary
Generations 3 and 4 monarch eggs are laid throughout the northern part of their range in July and August. Some adults move south in late July and August, and may lay eggs as late as October in the southern part of the US.
Some generation 3 monarchs emerge early enough to produce another summer generation. But those that emerge later are different from other monarchs in two important ways. First, they will migrate to and from the overwintering sites in Mexico. Second, they do not reproduce right after they emerge. In response to decreasing temperatures and shortening daylengths at the end of the summer, their reproductive organs remain in an immature state. Instead of mating and laying eggs, they spend their time drinking nectar and clustering together in nighttime roosts in preparation for their long journey south. This delayed maturity is called diapause. Most of the monarchs will remain in this condition until the following spring, when they begin to mate in the overwintering colonies.
During September, October and early November migratory adults fly to overwintering sites in central Mexico, where they remain from November to March.
In March, they begin to journey north, laying the eggs that will become the new Generation 1 along the way.
Generation 3 and 4 undergo huge increases in size, taking advantage of the abundance of milkweed and favorable temperatures in the northern US and southern Canada.