Annual Life Cycle

Generation 1 | Generation 2 | Generations 3 & 4

The monarchs that spend the winter in the mountains of central Mexico are the final generation of a cycle that begins anew each year. Most of the butterflies in this final generation begin their lives in the northern US or southern Canada, and then migrate thousands of kilometers to mountaintops that neither they nor their parents or grandparents have ever seen before. After spending several months in Mexico they return north, starting the cycle again as they lay eggs in northern Mexico and the southern US. Their parents, grandparents, and great-grandparents have very different lives. These summer monarchs live only about a month as adults and begin laying eggs when they are only a few days old.

In most years, the total number of monarchs probably increases with each generation. Because the winter generation must live for such a long time before reproducing, the entire population shrinks as some of these individuals die during the fall migration and overwintering period. The population then grows over the spring and summer.

Table 1. Summary of Monarch Annual Cycle
Generation #	Timing of immature stages*	Timing of adult stage*	Migrates?	Overwinter?
1	March - May	April- June	Yes, north in spring	No
2	May - July	June - July	No	No
3	July - August	July - August	Some	Some
4	July - October	August - April	Yes, south in fall and north in spring	Yes

*Months during which each generation exists.

Information for the following pages on monarch migration are taken from papers by S.B. Malcolm, B.J. Cockrell, and L.P. Brower and from data collected by the Journey North website.

Generation 1 | Generation 2 | Generations 3 & 4