Since 1935, researchers have observed and tracked monarch butterflies’ transcontinental journey to their winter home in Mexico. New technology from New Jersey-based Cellular Tracking Technologies now allows scientists to tag and track individual butterflies in real time. Monarch enthusiasts can follow these tagged insects on the free Project Monarch Science app.

The solar-powered tags weigh only 60 milligrams, which is 10 to 12 percent of a butterfly’s weight. Their signals are automatically detected within 300 feet of any of the billions of Bluetooth-enabled devices along the route. In 2025, more than 400 were deployed across the eastern United States and southern Canada.

Understanding monarchs’ habits and hazards is crucial for preserving these beautiful creatures, whose populations have declined by 22 percent over the past 20 years, according to a 2025 study published in Science.