Adriana Avelina Ruíz Márquez employs false eyelash adhesive to affix a miniature transmitter to the thorax of a monarch butterfly, just behind its head. The monarch, weighing approximately 0.5 grams, effortlessly carries the 60-milligram device, which incorporates a solar panel the size of a rice grain.
After the delicate procedure, which necessitates a toothpick and a Q-Tip, Ruíz Márquez releases the butterfly, and it swiftly takes flight by flapping its wings. This innovative tracking device, utilized for the first time in Mexico to tag monarchs before their migration back north to the U.S. and southern Canada, is anticipated to unravel some mysteries about these insects, with the aid of smartphones to monitor their movements.
The El Rosario butterfly sanctuary, located in Michoacán about 180 kilometers west of Mexico City, serves as the winter refuge for the majority of North America’s monarchs east of the Rocky Mountains. This sanctuary is one of six comprising the Monarch Butterfly Biosphere Reserve, spanning Michoacán and the State of Mexico, with a core protected area of around 135 square kilometers.
Teams from the federal Commission for National Natural Protected Areas and World Wildlife Fund (WWF) Mexico have tagged a total of 160 monarchs across the reserve, including 40 in El Rosario, with the new transmitters. This initiative will offer unprecedented insights into the initial leg of the butterflies’ migration north, according to biologist Eduardo Rendón Salinas from WWF Mexico.
The tracking project involves crowd-sourcing the trajectory of the butterflies using the microchipped transmitters. The Project Monarch app or a handheld receiver can be used to chart the butterflies’ path if nearby iPhones with Bluetooth and location functions enabled detect the signal.
Previously, scientists relied on wing tags attached to monarchs, which only revealed the tagging point and eventual discovery location. The new transmitters provide a higher level of spatial detail, offering a more nuanced understanding of the butterflies’ movements during migration.
The success of the previous trials paved the way for the transmitters to be utilized in a continent-wide monarch tracking project involving over 20 groups. The initiative commenced in Ontario in September 2025, with 30 monarchs tagged at the Long Point UNESCO biosphere reserve, south of Toronto.
From Canada to Cuba, a total of 400 monarchs were tagged by October, tracking their entry into Mexico’s Monarch Butterfly Biosphere Reserve in November. The reserve becomes the realm of the butterflies from November to March, with the monarchs forming massive clusters on oyamel branches. The community in El Rosario plays a crucial role in protecting and conserving this natural wonder, benefiting from tourism and sustainable practices.
The sanctuary thrives due to the collective efforts of the community, exemplifying the harmonious coexistence between humans and nature in preserving the monarch butterfly phenomenon.
