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monarch butterfly
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Monarch Butterfly Migration Underway

Every fall, tens of millions of monarch butterflies (Danaus plexippus) travel up to 3,000 miles in their migration—monarchs east of the Rocky Mountains make their way to central Mexico and those west of the Rockies fly to the California coast. These bright orange-and-black butterflies migrate farther than any other butterfly. As they return north in the spring, the monarchs mate, lay eggs on milkweed in the South, and die. After hatching, the next generation of caterpillars metamorphose and finish the journey.

tagging a monarch
People net and tag monarchs so we can learn about their migration patterns.
Traveling from southern Canada and across the U.S., monarchs fly up to 80 miles a day, stopping to feed on nectar and to rest. Many people delight in watching these vibrant butterflies pass through their neighborhood. Here at the Zoo, staff and visitors enjoy the occasional sighting.

Monarchs must reach their destination before it gets too cold or else they risk death. But cold weather is far from their greatest threat. Habitat destruction and harm to their food sources imperil this phenomenal migration.

Much of their spring and summer habitat in the U.S. has been ruined by new roads, housing developments, and expanding agriculture. Monarch larvae's only food source—milkweed—has been destroyed by people who consider it a harmful weed. Pesticides and herbicides threaten milkweed, nectaring plants on which the adults feed, and the monarchs themselves.

Their overwintering sites are in even more danger. The sites in California that offer them protection and everything else they need are also quite desirable to people for development. While some conservation measures are in place, property values and pressure to build continue to increase.

In Mexico, the monarchs spend the winter in only about a dozen sites—tens of millions blanket the trees in areas of just a few hectares each. Only some of these sites are protected from logging. Removing these valuable trees—for lumber, farming, and cattle grazing—destroys habitat and also creates gaps in the forest canopy, leaving roosting monarchs vulnerable. During two snowstorms in the the 1990s, millions of exposed monarchs died. Tourism encourages local people to leave the trees alone but is not as profitable.

As we learn more about monarchs, we can increase conservation efforts to protect them. Find out about tagging, butterfly gardens, milkweed, and more, visit the Monarch Watch website.