7 Amazing Facts About Monarchs As Fall Migration Begins In MI

The monarch butterfly migration, a breathtaking natural phenomenon where millions of the winged beauties fly up to 3,000 miles from Canada and the northern United States to the mountain forests of central Mexico, is or will soon be underway in Michigan.

Monarchs making their way south from the northern U.S. will spend about two months making their fall journey. Most monarchs typically begin leaving Michigan around Aug. 16. They typically finish their migration by mid to late September.

Monarch migration generally winds down in the United States by late October or early November. Most eastern monarchs head to wintering grounds in central Mexico, while western monarchs may spend the winter in groves along the California coast. Monarchs also occur year-round in South Florida.

An Unsolved Monarch Mystery

The generation that migrates is unlike the generations before it. Most monarchs born in spring and summer live only two to five weeks, but the late-summer and fall “super generation” can live six to nine months. That one long-lived generation makes the trip south, survives the winter and starts the journey north again in spring.

Scientists know monarchs use an internal clock and the sun to orient themselves, and research suggests they may also use Earth’s magnetic field. But exactly how inexperienced butterflies from places as far apart as New England, the Midwest and Canada make it to the same small mountainous overwintering region used by generations before it remains one of nature’s great mysteries.

They Hitch Rides

Monarchs sometimes ride air currents a mile above the ground — roughly 5,280 feet, an altitude reached by migrating birds and well within the cruising range of small aircraft. The U.S. Fish & Wildlife Service specifically notes that monarchs can catch rising air currents and sometimes fly a mile high.

A monarch can cover far more ground than the migration itself advances in a day. The overall migration front moves about 25-30 miles southward per day, but individual monarchs can travel hundreds of miles in only a few days when winds are favorable.

Monarch Watch says one tagged late-season monarch averaged 61 miles a day for two weeks traveling from Virginia to Texas. It also says some tagged butterflies have covered hundreds of miles in only a few days when the weather cooperated.

They barely have to flap their wings when conditions are right. Monarch Watch says that with favorable tail or quartering winds, a gliding monarch may maintain altitude by flapping just once every 20 to 30 feet. Its glide ratio is roughly 3-to-1 or 4-to-1, meaning it can travel three or four feet forward for every foot it descends.

They Need Fuel

Monarchs migrate on fat reserves — and soaring saves an astonishing amount of fuel. Monarchs gorge on flower nectar during migration, converting its sugars into fat. Traveling south is hard work. They’d rather not flap their wings if they don’t have to.

Biologist David Gibo calculated how far a monarch’s energy reserves could take it using powered flight compared with soaring and gliding. Using a butterfly carrying 140 mg of stored fat as the example, he estimated that the reserve could support about 44 hours of continuous flapping flight.

When the butterflies had to flap their wings, they ran out of fuel after 44 hours of flight. Relying largely on soaring and gliding, that same energy reserve could theoretically support about 1,060 hours of flight, nearly 25 times longer.

You Can Help

Monarchs are trying to gain weight along the way. Nectar's carbohydrates are converted to fat stored in the abdomen, and those reserves both fuel migration and help sustain the butterflies through the winter in Mexico. Monarch Watch notes that two otherwise similarly sized monarchs can differ in mass by as much as 40 percent, largely because of differences in stored reserves

They can actually gain weight during a 3,000-mile migration. Instead of steadily burning through their reserves, monarchs stop at flowers along the route and convert nectar sugars into fat. Monarch Watch says many monarchs gain mass as they migrate south because they need enough stored fat not only to reach Mexico but also to survive the winter and begin the return trip north.

During fall migration, adults need nectar-rich flowers to fuel the trip and build fat reserves for winter. Late-blooming goldenrods, asters, blazing stars and other native flowers can become refueling stations.

Even in late summer, leaving blooming plants standing — or adding nursery-grown plants already in flower — can help passing monarchs.

They’re Not That Fragile

Monarch wings aren't as fragile as they look.

Their wings can withstand ordinary rain, and the butterflies tuck themselves beneath leaves and into sheltered trees when storms approach. But once their wings become thoroughly wet, they can't fly and have to wait for them to dry — making prolonged cold, wind and heavy rain potentially deadly.

The wings themselves aren't tissue-paper delicate. They're made of a thin membrane supported by veins and covered with thousands of microscopic scales. Losing some scales is normal, and monarchs can keep flying with considerable wear. But wings don't repair themselves. Wind, hail, rain, collisions and age can fray or tear them, and serious damage can eventually interfere with flight.

What can really hurt monarchs is the combination of prolonged rain, cold and wind. They become unable to fly, can be knocked out of roosts, and may be exposed for long periods without feeding. U.S. Fish and Wildlife says they can withstand some rain and even freezing conditions, but not prolonged exposure.

At their Mexican wintering grounds, severe storms have caused enormous mortality; Monarch Watch reports that a 2002 storm beginning with about 48 hours of rain killed an estimated 80 percent of the overwintering population.

A Colorful Monarch Airbnb

Migrating monarchs often gather by the dozens, hundreds or even thousands in trees to roost overnight, making branches look as if they are blanketed in vibrant autumn leaves, featuring dense, shimmering clusters of bright orange and black

With their wings folded, they are sometimes packed so densely that individual butterflies are hard to distinguish. As the morning sun warms them, the monarchs begin opening their wings, turning the roost bright orange before lifting off and continuing south.

Monarchs need to warm up before taking off. Their flight muscles have to reach roughly 86 degrees for sustained flight, so cool mornings can keep migrating monarchs grounded until the sun warms them.

Day Of The Dead Arrival

Their arrival coincides with the Day of the Dead. Monarchs begin reaching central Mexico around the end of October, just as families prepare for Día de los Muertos on Nov. 2.

For generations, that timing has carried spiritual meaning for Indigenous communities in the region. UNESCO says the Purépecha regard monarchs as the souls of the dead, and their annual arrival as a sign that deceased loved ones are returning to visit.

Among Mazahua and Otomí peoples, monarchs have also been associated with the agricultural calendar; UNESCO notes they are known as “the harvester” because they arrive around the time fields are being prepared for planting.