It’s early November, and Pacific Grove is preparing for thousands of visitors.

Calling itself “Butterfly Town, USA,” the small community on California’s Monterey Peninsula has already held its annual Butterfly Parade, where local schoolchildren dress up like the insect. Currently, past a sign announcing “Caution: Butterfly Zone” and adjacent to the Butterfly Grove Inn, the Monarch Grove Sanctuary is hosting approximately 1,000 monarch butterflies that have arrived early to spend their winter in this 2.4-acre site.

A volunteer butterfly docent for the Pacific Grove Museum of Natural History, Jack Beigle helps human visitors spot the monarchs clustered on a stand of nearby eucalyptus trees. “They look like dead leaves in a U-shape,” he says, as he points a spotting scope towards the trees. “They are all butterflies.”

He’s right. Above the tree trunks is a congregation of what at first appear to be clumps of dead leaves. But then a breeze causes the monarch butterflies to flutter their wings—revealing a blast of bright orange color.

Nearby, several butterflies float up into the sky. “We have a few flying,” Beigle says. “They can’t fly if their temperature gets below 55 degrees.”

Warmer winter temperatures bring monarch butterflies to almost 200 overwintering sites on the California coast, including Pacific Grove’s Monarch Grove Sanctuary, Santa Cruz’s Natural Bridges State Park, and the state’s largest site for vacationing butterflies, the Pismo Beach Monarch Grove. The butterflies will stay along the coast from November through February.

As brightly colored monarchs float from the sky like confetti, Beigle explains the insects’ amazing journey. The monarch butterflies have chosen this small swath of land in Pacific Grove for its mix of moderate temperature, humidity, and shelter from the wind.

Beigle says that the butterflies have traveled to Pacific Grove from 100 to 1,000 miles north and east of Pacific Grove. Most monarchs fly to the coast from the foothills of the Sierra Nevada mountains on the border between California and Nevada. In early spring, the butterflies will migrate back to their cooler homes in the Sierra Nevada.

Beigle lists a few facts about the migrating monarch that elicit gasps from the small crowd of people gathered around him. He notes that some monarchs have been clocked flying at 15 miles per hour in still air. They also have stamina: “Two hundred miles in a day is common,” he says. “It depends on the wind.”

Monarchs are also high fliers. “Pilots have even reported seeing them at 10,000 feet,” he says.

While the migration of North America’s west coast population of monarch butterflies is impressive, it’s the eastern population of the species that achieves one of nature’s greatest feats. (The two monarch populations are separated by the Rocky Mountains.)

The eastern population journeys all the way from the northeast corner of the United States and Canada to a single location in central Mexico’s Michoacán state. The migration for the insect can be up to 3,000 miles.

Migration Mystery

One aspect of the monarch butterfly’s migration that has long puzzled scientists is how the tiny insects navigate such extended journeys. A neurobiologist at the University of Massachusetts Medical School, Dr. Steven Reppert, has been researching the monarch butterfly’s migration for years.

Reppert believes the insects use the sun, or rays of the sun, to determine their location. Specific chemical proteins in the butterfly’s brain help it to use the sun as a compass. Monarchs can interpret the sun’s position in the sky to help them fly from the northern United States, through Texas, and into Michoacán.

University of Minnesota professor Karen Oberhauser has studied the monarch butterfly for 25 years. Oberhauser is still amazed that an animal the weight of a single paper clip can complete such a long journey.

“I think the most impressive thing is that something that size can fly that far and find a specific spot in the mountains of Mexico, leaving this large, large area and congregating in this very small area,” she says.

Oberhauser is concerned about obstacles to the migrating monarch butterfly. “Probably the worst danger they can encounter is a lack of habitat, because they need to eat while they are migrating,” she says.

Monarchs’ favorite food is milkweed, which many farmers and homeowners consider a pest. “If all [the butterflies] are going over is agriculture fields and cities and suburbs with lawns, they are not going to find anything to eat. Probably the greatest cause of mortality during the migration is starving to death.”

The eastern population of the monarch butterfly not only travels farther than the western population, more butterflies make the trip. According to Oberhauser, an estimated half a billion monarchs spend the winter in central Mexico.

“All of the butterflies in all of the overwintering sites along the coast of California are many, many fewer than the butterflies in the Mexican overwintering sites,” Oberhauser says.

Back in Pacific Grove, Beigle impresses a small crowd with more information about the western monarch butterfly migration while being sure to mention the even larger journey occurring on the other side of the Rocky Mountains.

“We feel good when we get 40,000 to 50,000 butterflies here,” he says. “They get millions down in Mexico.”

Monarch Migration Mystery
Those aren't a clump of dead leaves; they're a clump of monarch butterflies.

Watch Out
Monarch butterflies' distinctive bright orange coloring is a warning to predators such as birds and reptiles. Monarchs are bad tasting and upset predators' digestive systems.

Family Vacation
According to National Geographic, only monarchs born in late summer or early fall make the winter migration, and they make only one round trip. By the time next year's winter migration begins, several generations will have lived and died and it will be the great-grandchildren of last year's migrators that make the trip. Yet somehow these new generations know the way and follow the same routes their ancestors tooksometimes even returning to the same tree.

achieve
Verb

to accomplish or attain.

adjacent
Adjective

next to.

Noun

the art and science of cultivating land for growing crops (farming) or raising livestock (ranching).

amaze
Verb

to greatly surprise or astonish.

annual
Adjective

yearly.

billion
Noun

1,000,000,000

breeze
Noun

light wind or air current.

Noun

edge of land along the sea or other large body of water.

Noun

instrument used to tell direction.

concern
Verb

to worry or take an interest in.

confetti
Noun

small bits of paper, usually brightly colored, thrown or dropped during a festival or celebration.

congregate
Verb

to gather.

determine
Verb

to decide.

docent
Noun

knowledgeable guide.

encounter
Verb

to meet, especially unexpectedly.

estimate
Verb

to guess based on knowledge of the situation or object.

eucalyptus
Noun

tree native to Oceania.

extend
Verb

to enlarge or continue.

feat
Noun

accomplishment or achievement.

foothill
Noun

hill at the base of a mountain.

Noun

environment where an organism lives throughout the year or for shorter periods of time.

Noun

amount of water vapor in the air.

impressive
Adjective

admirable or very memorable.

insect
Noun

type of animal that breathes air and has a body divided into three segments, with six legs and usually wings.

journey
Noun

voyage or trip.

lawn
Noun

area of grass mowed, watered, and maintained by people.

migrate
Verb

to move from one place or activity to another.

milkweed
Noun

plant that is an important source of nectar for many insects. Also called silkweed.

monarch butterfly
Noun

insect native to North America.

mountain
Noun

landmass that forms as tectonic plates interact with each other.

navigate
Verb

to plan and direct the course of a journey.

neurobiologist
Noun

person who studies chemical reactions in the brain.

obstacle
Noun

something that slows or stops progress.

occur
Verb

to happen or take place.

overwintering site
Noun

winter destination of a migrating animal.

pest
Noun

harmful or annoying person or thing.

protein
Noun

one of many complex compounds, made of chains of amino acids, that make up the majority of all cellular structures and are necessary for biological processes.

research
Noun

scientific observations and investigation into a subject, usually following the scientific method: observation, hypothesis, prediction, experimentation, analysis, and conclusion.

specific
Adjective

exact or precise.

spotting scope
Noun

small telescope used for short distances during daylight hours.

stamina
Noun

strength and power to endure difficulty.

suburb
Noun

geographic area, mostly residential, just outside the borders of an urban area.

swath
Noun

path or line of material.

Noun

degree of hotness or coldness measured by a thermometer with a numerical scale.

volunteer
Noun

person who performs work without being paid.