Adriana Avelina Ruíz Márquez affixes a mini transmitter to the thorax of a monarch butterfly using fake eyelash glue, positioning it just behind the butterfly’s head. The monarch butterfly, weighing approximately half a gram, effortlessly carries the 60-milligram device, equipped with a solar panel the size of a grain of rice. Following a delicate procedure involving a toothpick and a Q-Tip, Ruíz Márquez releases the butterfly, which promptly takes flight by flapping its wings.
The tracking device, a new innovation utilized for the first time in Mexico to tag monarch butterflies before their migration to the U.S. and southern Canada, is expected to unravel mysteries surrounding the insects. Ruíz Márquez anticipates leveraging people’s smartphones to monitor the butterflies’ movements, shedding light on enigmatic aspects such as their migration routes and behavior upon arrival and departure.
In the El Rosario butterfly sanctuary, where dense clusters of butterflies fill the air akin to mosquitos and blackflies in Canadian marshlands at dusk, Ruíz Márquez operates amid patches of sunlight filtering through the canopy of towering oyamel firs. This sanctuary, nestled in Michoacán state about 180 kilometers west of Mexico City, serves as a crucial overwintering site for the vast majority of North America’s eastern monarchs.
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 cutting-edge transmitters. Eduardo Rendón Salinas, a biologist with WWF Mexico, emphasizes the significance of capturing detailed insights into the initial leg of the monarchs’ journey northward.
The monarch butterflies embark on a multi-generational migration spanning up to 5,000 kilometers. The so-called super generation, emerging in late summer from regions like the Prairies and Maritimes down to the U.S. Northeast and Midwest, undertakes a non-stop journey southward. This generation reproduces in sanctuaries such as El Rosario before initiating their northward migration, laying eggs for the subsequent generation en route.
A novel microchipped transmitter emits signals detectable by nearby iPhones, enabling crowd-sourced tracking of the butterflies’ trajectory when Bluetooth and location functions are activated. The Project Monarch app, accessible for download by anyone, or a handheld receiver can assist in mapping the butterflies’ path with unprecedented spatial precision. David La Puma, director of global market development at Cellular Tracking Technologies, the firm behind the device, underscores the enhanced tracking capabilities compared to traditional wing tags.
The project has evolved from successful pilots in previous years to a continent-wide initiative involving over 20 groups, commencing in Ontario in September 2025. By October, 400 monarchs tagged from Canada to Cuba were monitored entering Mexico’s Monarch Butterfly Biosphere Reserve. The reserve, transformed into a realm dominated by the butterflies between November and March, is vigilantly safeguarded by community patrols to deter illegal activities like logging.
The El Rosario community, which collectively manages the ejido housing the sanctuary, has established a flourishing tourism enterprise that sustains them during the monarchs’ winter stay. Additionally, they cultivate oyamel seedlings to preserve the forest’s health, embodying a deep sense of responsibility towards their natural heritage and the remarkable monarch butterflies.