As monarchs return north in the spring, they lay eggs and milkweed along the way. These larvae appear in the southern return path in March and early April. This generation will also migrate north, following their parents. By August to early September, three to four generations have evolved. The younger monarchs take the place of those who have died along the way, and the cycle continues.
A Dangerous Journey
Monarchs encounter many dangers along their migration path. Storms, predators, humans, cars, and fatigue will prevent thousands from ever reaching their destination. Upon arriving at their winter retreats, they’ll find even greater danger. Cold temperatures, strong winds, and snow will wipe out 40 to 60% of the population during the winter.
So why do monarchs participate in this dangerous migration cycle at all? Unfortunately, scientists have not found a definitive answer. The leading theory is that monarchs are attempting to follow the distribution of a specific genus of milkweed called Asclepias, which provides the primary food source for monarch larvae.
In many parts of the world, humans are undertaking efforts to conserve monarch butterfly populations. The most important method of monarch conservation is the protection of monarch habitats. In Mexico and Canada, humans have constructed butterfly reserves that offer a safe place for monarchs to live and reproduce, increasing their chances of survival. The protection of milkweed, the monarch’s primary food source, is also a vital component of monarch conservation.