Tiny Trackers Reveal the Secret Routes of Monarch Butterflies on Their 4,800km Journey to Mexico

Every autumn, millions of orange-and-black monarch butterflies set off on one of the longest journeys in the insect world. They fly up to 4,800 kilometres from Canada and the United States to spend the winter in the mountain forests of central Mexico. It is a journey no single butterfly has ever made before, because the butterflies that arrive in Mexico are the great-great-grandchildren of the ones that left the year before.

For years, scientists knew where the journey started and where it ended, but much of the middle was a mystery. Where exactly do the butterflies stop to feed and rest? Which routes do they take? And do the monarchs from the west of North America ever meet the ones from the east?

Now, tiny solar-powered trackers are finally giving answers. This year, scientists fitted nearly 1,750 monarch butterflies with the miniature devices, and about 175 of them have already been detected in Mexico. The early results are surprising researchers and rewriting what we thought we knew about this famous migration.

What scientists are doing

The project is called Project Monarch Science. It is a joint effort by researchers and conservation groups across North America, including the National Wildlife Federation. Members of the public can also take part, by following individual butterflies on a free mobile app of the same name.

The work is led by Rebeca Quiñonez-Piñón, a senior scientist at the National Wildlife Federation. She has spent years wondering where monarchs stop for a meal and a night’s rest during their long migration across the continent. The new trackers are helping her find those places before they disappear.

Tracking began last year, and this year’s effort is much bigger. Nearly 1,750 butterflies were fitted with the tags before they set off south. The tags send out radio signals that are picked up by receivers along the way, and by smartphones running the Project Monarch Science app. Each time a tagged butterfly passes near a receiver, scientists learn where it was and when.

How the tiny trackers work

The most remarkable part of the project is the size of the trackers. Each one costs around $200 and weighs only about 60 milligrams, roughly as much as a drop of water. That is light enough to be attached to a butterfly without slowing it down or stopping it from flying.

The tags were developed by a company called Cellular Tracking Technologies. They are solar-powered, so they keep working as long as the butterfly is out in daylight. They send signals on a radio frequency similar to Bluetooth, the same kind of wireless technology used by headphones and smart watches.

There is one limit to the technology. The tags do not give a butterfly’s exact location, like a GPS device would. Instead, they show where a receiver picked up the signal. Scientists therefore know that a butterfly passed through a particular area, even if they do not know its precise path through it. Even so, this is far more detail than researchers have ever had before.

In the past, scientists tracked monarchs by sticking tiny paper tags on their wings and hoping someone would find them later in Mexico. That method could only tell them where a butterfly ended up, not how it got there. The new electronic tags show the journey itself, stop by stop.

What the trackers have found so far

Since this year’s migration began, about 175 tagged butterflies have been detected in Mexico. That is roughly one in every ten of the butterflies that were tagged. The number is expected to grow as more butterflies complete the journey and pass near receivers.

Some of the findings are already changing the picture of monarch migration:

A butterfly from Utah joined the eastern monarchs. Since tracking began last year, scientists found the first evidence of a butterfly from Utah, west of the Rocky Mountains, joining the eastern monarchs in central Mexico. Until now, researchers thought the western and eastern monarch populations mostly stayed apart. This butterfly showed that the two groups can mix.

Some monarchs crossed the Gulf of Mexico. Other tagged butterflies travelled down the Eastern Seaboard of the United States to Florida, then flew across the Gulf of Mexico and are now being tracked across Mexico. Scientists had not seen this connection in such numbers before. Crossing open water is a long, risky flight for an insect that weighs less than a gram, and the trackers prove that many monarchs do it.

The journey is longer and more varied than expected. The results show that monarchs do not all follow one single route south. Different butterflies take different paths, and the routes can cross in ways nobody had mapped before.

Why stopover places matter

The main goal of the project is not just to draw lines on a map. It is to find the places where monarchs stop to feed and rest, and to protect those places before they are lost.

A monarch butterfly cannot fly 4,800 kilometres without stopping. Along the way it needs flowers to drink nectar from, so it has the energy to keep going. It also needs safe places to spend the night, sheltered from wind and cold. Scientists call these places stopovers, and they are as important to the migration as the winter forests in Mexico.

The problem is that many stopover places are disappearing. Fields of wildflowers are being ploughed up, built on, or sprayed with weed killer. When a stopover disappears, the butterflies that depended on it may not have the energy to finish the journey.

This is why Quiñonez-Piñón is leading a study that combines the tracking data with community science to learn where monarchs stop in Texas. Texas is a funnel for the migration: monarchs from across the eastern United States pass through the state on their way to Mexico. If scientists can map the key stopover sites in Texas, conservation groups can work to protect them, for example by planting native wildflowers and milkweed, the plant monarch caterpillars feed on.

Emma Pelton, a senior conservation biologist with the Xerces Society for Invertebrate Conservation, is one of the scientists involved in the wider effort. The Xerces Society works to protect invertebrates, the animals without backbones, including butterflies, bees and other pollinators.

The destination: forests of fir trees

The monarchs that survive the journey end up in the oyamel fir forests of central Mexico. There, millions of butterflies cluster together on the trees, covering the branches in orange and black. The forests are a protected biosphere reserve and a UNESCO World Heritage site.

The butterflies spend the winter there, barely moving, living off the fat they stored during the journey. In the spring, they begin the journey north again, laying eggs on milkweed plants along the way. It takes several generations of butterflies to reach Canada again by the summer. Then, in the autumn, a new generation sets off south, guided by instincts and signals from the sun and the Earth’s magnetic field that scientists are still trying to fully understand.

How you can follow the butterflies

One of the most unusual parts of Project Monarch Science is that anyone can take part. The public can follow the progress of individual tagged butterflies through the free Project Monarch Science app. When a butterfly is detected by a receiver, its journey appears on the app for everyone to see.

Community scientists, ordinary people who help with research, also play a big part. Volunteers help tag butterflies, report sightings, and plant the wildflowers and milkweed that monarchs need. The tracking project shows that protecting a migration is not only a job for scientists in laboratories. It depends on people all along the route, from Canada to Mexico, looking after the small patches of habitat that the butterflies need to survive.

Why this migration matters

The monarch migration is one of the great natural wonders of the world. No other butterfly travels so far, and no other insect migration involves so many generations. The eastern monarch population has fallen sharply over recent decades, largely because of the loss of milkweed and wildflower habitat, and changes in farming and land use.

That is why the tracking matters. For the first time, scientists can see the whole journey, not just the start and the finish. They can find the places that matter most, and they can show governments, farmers and the public exactly where help is needed.

The trackers are still sending signals as more butterflies arrive in Mexico. Each new detection adds another piece to the map of a journey that has puzzled scientists for generations. And for the first time, the butterflies are telling us the route themselves.

Frequently Asked Questions

How far do monarch butterflies migrate?

Eastern monarch butterflies travel up to 4,800 kilometres (about 3,000 miles) from southern Canada and the United States to the oyamel fir forests of central Mexico, where they spend the winter.

How do scientists track monarch butterflies?

Scientists attach tiny solar-powered radio tags, weighing about 60 milligrams, to the butterflies. The tags send signals that are picked up by receivers and by smartphones running the Project Monarch Science app. Each tag costs around $200 and was developed by Cellular Tracking Technologies.

How many monarchs were tagged this year?

Nearly 1,750 monarch butterflies were fitted with trackers in 2026, and about 175 of them had been detected in Mexico since the migration began.

What have the trackers discovered?

They have shown that a butterfly from Utah, west of the Rocky Mountains, joined eastern monarchs in central Mexico, and that other monarchs travelled down the east coast of the United States to Florida, crossed the Gulf of Mexico, and continued across Mexico. These connections had not been seen in such numbers before.

Can I follow a monarch butterfly myself?

Yes. The public can follow individual tagged butterflies on the free Project Monarch Science app, which shows their progress as they are detected by receivers along the migration route.

Why are monarch numbers falling?

The eastern monarch population has declined over recent decades, mainly because of the loss of milkweed, the only plant monarch caterpillars eat, and the loss of wildflowers that adult butterflies feed on. Protecting stopover sites along the migration route is one of the main aims of the tracking project.

Sources

• Bastille Post (AP), “Monarch butterflies get tiny trackers to help scientists follow their mysterious migration”: https://www.bastillepost.com/global/article/6318940-monarch-butterflies-get-tiny-trackers-to-help-scientists-follow-their-mysterious-migration
• Weather.com (AP), “Monarch butterflies get tiny trackers to help scientists follow migration”, 4 November 2026: https://weather.com/2026/11/04/science/nature/wild-animals/monarch-butterflies-trackers-track-migration
• The Times of India, “Scientists fitted nearly 1,750 monarch butterflies with tiny solar-powered trackers”: https://timesofindia.indiatimes.com/science/scientists-fitted-nearly-1750-monarch-butterflies-with-tiny-solar-powered-trackers-to-follow-their-migration-across-north-america-about-175-have-been-detected-in-mexico-as-researchers-map-previously-uncertain-routes/articleshow/135565337.cms
• DT Next, “Flight paths: Tiny trackers aim to unravel monarchs’ migration mystery”: https://www.dtnext.in/edit/flight-paths-tiny-trackers-aim-to-unravel-monarchs-migration-mystery

This article is for general information and education only. It is not legal or financial advice.