Scientists fitted nearly 1,750 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

Have you ever watched a butterfly pass by and wondered where it was headed? With their distinctive colours and wing patterns, butterflies have a way of catching our attention and, lately, the attention of scientists in particular. According to U.S. News & World Report, Rebeca Quiñonez-Piñón and other scientists are now getting a closer look at one of North America’s most fascinating journeys in nature, with the help of tiny solar-powered devices attached to monarch butterflies. Nearly 1,750 of these orange and black insects were fitted with trackers this year, helping researchers follow their movements as they travel south towards their wintering grounds in Mexico.The effort is part of Project Monarch Science, a free mobile app developed through a collaboration involving researchers and conservation organisations working across North America. While monarch migration has been studied for decades, scientists have often struggled to establish the precise routes individual butterflies take, how far they travel in a day and where they stop to rest or feed along the way. The new tracking technology is helping fill some of these research gaps, with around 175 tagged butterflies already detected in Mexico during this year’s migration.

Tracking monarchs across North America

Monarch butterflies are known for their long-distance seasonal movements, with some travelling nearly 3,000 miles (4,800 kilometres) from southern Canada and the United States to forests in central Mexico. Their wintering destination includes protected areas where the insects gather in large numbers on oyamel fir trees, covering branches and trunks in clusters. The journey is particularly remarkable considering the size of the butterflies and the number of environmental conditions they must navigate along the way.For researchers, however, knowing that monarchs make this journey is only the beginning. Understanding how they get there and what happens during the thousands of miles in between is equally important. Older tracking devices were often too heavy to be attached to such small insects without raising concerns about their movement. The newer transmitters developed by Cellular Tracking Technologies are much smaller, costing around $200 each and weighing approximately 60 milligrams, about as much as a drop of water.

What the transmitters help with

The devices are solar-powered radio transmitters that operate at the same frequency as Bluetooth technology. They send out signals that can be detected by compatible receivers and smartphones running the Project Monarch Science app when a tagged butterfly passes within range. These detections are then added to a growing record of its movements, helping researchers piece together the routes it has travelled. People can also follow individual butterflies through the free app, making the research accessible beyond laboratories and field stations.

(Image credit: Canva)

However, attaching the devices requires a lot of care, with researchers and trained community scientists first selecting butterflies that are large and strong enough to carry the added weight. The insects are gently secured on a specially designed board while the transmitter is attached to their bodies using adhesive. Their legs, antennae and wings are protected throughout the process before they are released to continue their migration.Researchers have recorded monarchs travelling from Utah, west of the Rocky Mountains, towards their wintering grounds in central Mexico, with their movements revealing connections with butterflies from the eastern population. Some of these early findings have therefore highlighted an intriguing connection between migration routes that scientists had previously suspected but could not confirm at this scale. Other tracked insects have travelled down the Eastern Seaboard towards Florida before crossing the Gulf of Mexico and continuing through the country.Going forward, one of the areas researchers are particularly interested in is the so-called Texas funnel, a narrow corridor through which many monarchs east of the Rocky Mountains travel during their seasonal migration.