Every fall, monarchs from eastern North America join their wintering grounds in Mexico. The following spring, survivors returned north and re-breeded. However, a single butterfly does not close the annual circuit by coming back wherever it has gone: other generations take over.
The descendants of the overwinterers continue the progression towards the more northern breeding regions. Other births occur during the beautiful season. The butterflies that will then undertake the autumn journey therefore belong to later generations. The exact number varies with the places, conditions and overlap of the generations; too rigid a calendar would distort this story.
There are no family convoys where the elders personally show the way to the young. The global itinerary emerges from seasonal patterns and cycles divided among different individuals. To understand this migration, it is necessary to follow a population in time: the map represents a journey, but this journey exceeds the lifetime of its participants.
What we know
The number of generations is not constant.
To go to the source
References consulted on September 21, 2026. Linked pages may be in another language.
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