FASTFACTS

AREA COVERED:

Up to 5,600 miles round trip.

HABITAT:

North and South America, Atlantic and Pacific islands, western Europe.

PREDATORS:

Frogs, lizards, mice, birds.

INDIVIDUAL HERD POPULATION:

About 100 million in the Canada-to-Mexico set.

MONARCH BUTTERFLY IN-DEPTH

More from NationalGeographic.com

MONARCH BUTTERFLY (Danaus plexippus)

The monarch butterfly is one of two members of the genus Danaus. (The other is the queen butterfly, Danaus gilippus. ) It is is found in many parts of the world, from Australia to North and South America. Monarch butterflies need warmth to survive. The two distinct populations in North America—one in the East, one in the West—both leave their breeding grounds each fall and race southward to avoid the killing frost. Eastern monarchs head to the mountains of central Mexico, while the western monarchs spend the winter along the California coast.

According to Kansas University monarch expert Orley “Chip” Taylor, most of the monarchs joining the migration each fall are three-to-four generations removed from those that made the journey the previous year. While butterflies that breed during the summer live for just two to five weeks, migratory monarchs that survive the winter in Mexico reach eight to nine months of age and may have the greatest longevity of all butterflies.

Monarchs’ migration progresses southward at a pace of about 25 to 30 miles a day, though individual butterflies often fly further when conditions permit, according to Taylor. Monarchs are believed to navigate by using the sun and a circadian clock located in their antennae. Along the way, they must contend with multiple perils, from weather to birds that become immune to the poison, created by monarch larvae’s feeding on milkweed, which discourages predators from eating them.

Human activity poses a increasing threat to the monarch butterfly’s continued survival, according to Taylor. Both the milkweed plants needed by larvae and the nectar sources that fuel the adults’ reproduction and migration are diminishing due to chemically-intensive agriculture and excessive mowing and use of herbicides in roadside areas in North America. That habitat loss may be related to the reduced numbers of overwintering monarchs observed in recent years.

Monarchs play an important role in nature, because adults feed on flower nectar and in the process pollinate many plants.