Adriana Avelina Ruíz Márquez carefully attaches a miniature transmitter, powered by a solar panel the size of a grain of rice, to the thorax of a monarch butterfly using fake eyelash glue just behind its head. The monarch, weighing approximately half a gram, effortlessly carries the 60-milligram device. After the delicate operation, which involves a toothpick and a Q-Tip, Ruíz Márquez releases the butterfly, and it swiftly takes flight by flapping its wings.
This new tracking device, utilized for the first time in Mexico to tag monarch butterflies before their migration back north to the U.S. and southern Canada, is expected to unravel mysteries surrounding the insects. Ruíz Márquez expressed optimism that by leveraging people’s smartphones, they can track the movements of the butterflies and gain insights into their migration patterns and behaviors.
In the El Rosario butterfly sanctuary, where sunlight filters through the branches of towering oyamel firs, thick clusters of butterflies whirl like mosquitos and blackflies at dusk. This sanctuary, located in Michoacán about 180 kilometers west of Mexico City, is one of six sanctuaries within the Monarch Butterfly Biosphere Reserve, spanning Michoacán and the State of Mexico with a core protected area of approximately 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, with 40 in El Rosario, using the innovative transmitters. This initiative aims to provide a detailed understanding of the butterflies’ initial migration northward. Eduardo Rendón Salinas, a biologist with WWF Mexico, emphasized the importance of tracking monarchs between colonies, a phenomenon previously only theorized.
The monarch butterflies undertake an arduous journey north spanning up to 5,000 kilometers, requiring three to four generations to complete. The super generation of monarchs, emerging in late summer, migrates from the Prairies to the Maritimes, down through the U.S. Northeast and Midwest, before returning south in one continuous trip.
The microchipped transmitters emit signals detectable by nearby iPhones, enabling crowd-sourced tracking of the butterflies’ trajectory if Bluetooth and location functions are activated. This technology, facilitated by the Project Monarch app or a handheld receiver, offers unprecedented spatial detail previously unattainable with wing tags.
David La Puma, director of global market development at Cellular Tracking Technologies, the developer of the device, highlighted the enhanced precision in monitoring butterfly movements during migration. Future upgrades to the transmitter will enable Android smartphones to serve as passive detectors, expanding the scope of tracking capabilities.
Following successful pilot programs in 2023 and 2024, the transmitters were integrated into a continent-wide monarch tracking project involving over 20 groups. The initiative, launched in Ontario in September 2025 with the participation of Environment and Climate Change Canada and Birds Canada, tagged 30 monarchs at the Long Point UNESCO biosphere reserve in Ontario.
The monarchs, tagged from Canada to Cuba, were tracked entering Mexico’s Monarch Butterfly Biosphere Reserve in November. The sanctuary, particularly in the period between November and March, transforms into a haven for the butterflies, with massive clusters enveloping the oyamel branches under the watchful protection of the local community.
The El Rosario ejido, managed collectively by the community, sustains a vibrant tourism industry during the monarchs’ wintering period, providing essential income. Additionally, the community nurtures oyamel seedlings, ensuring the forest’s well-being and preserving the natural wonder of the monarch butterfly.