Among A Sea Of Monarch Butterflies In Mexico — The Most Magical Thing I’ve Ever Seen (35 New Pics)

The duration of this journey is much longer than their natural lifespan, so the butterflies that return after wintering are often the second—or even later—generation. Great-grandchildren. Those born at the beginning of summer live for about two months, while those born at the end of summer enter a special state called diapause before beginning their winter migration.

Diapause is a non-reproductive phase during which butterflies enter a physiological state of torpor that slows down the aging process, allowing them to survive the winter. Therefore, the butterflies gathered in the Biosphere Reserve in the state of Michoacán are not truly living their full lives but exist in a kind of suspended animation—though they still fly quite actively.

I do not recommend visiting the reserve on days without sun; during cloudy weather, the butterflies sit motionless, clustered on branches and on each other. They need warmth to fly. Many tourists leave disappointed if they visit on overcast days.

In spring, when the butterflies awaken, they reproduce. The caterpillar and pupa stages each last about two weeks, after which adult butterflies—the descendants of those that migrated in autumn—begin their journey north. Along the way, they lay eggs and then die. Their offspring continue the flight, breeding again during migration. The great- and great-great-grandchildren of the butterflies that left for warmer climates in autumn eventually return home. The second, third, and fourth generations of these insects make their way back to the northern regions of the United States and Canada.

The monarch is one of the few insects capable of crossing the Atlantic Ocean.

The largest populations are found in North America, but monarchs can also be seen in Africa, Australia, and parts of Europe—such as Sweden and Spain. They have been spotted in the far southwest of Great Britain, near Lake Bennington, in Walla Walla (Washington), the Far East, New Zealand, North Africa, and the Hawaiian Islands. Permanent populations live in Bermuda, Florida, Arizona, and the Caribbean, where the climate remains mild year-round.

People often ask why birds don’t eat these large clusters of monarchs. The answer lies in their diet: the milkweed plant, which monarch caterpillars feed on, is both poisonous and foul-tasting to birds. Its sap contains cardenolides—compounds that not only taste unpleasant but can also cause nausea in small amounts and even heart failure in larger doses. The toxin absorbed from the plant’s leaves remains in the caterpillar’s body (their bright colors serve as a warning of their toxicity) and is retained after metamorphosis, spreading throughout the adult butterfly’s body.

Thanks to this natural defense, colonies of monarchs in their suspended state survive the winter largely undisturbed—since birds prefer to feed on less toxic insects.