During Autumn, millions of monarch butterflies fly up to 3,000 miles from southern Canada and the northern U.S. to mountain forests in central Mexico. Scientists usually rely on wing tags and broad population counts to remap their migration path. Now, researchers and citizens can use Project Monarch to watch the butterflies’ journey via smartphone detections and tiny solar-powered transmitters.

Project Monarch uses BlūMorpho, a solar-powered, digitally coded radio tag developed by Cellular Tracking Technologies. At just 60 mg, the tracker doesn’t need a battery to run and transmits an identification signal on the 2.4-GHz band also used by Bluetooth. Scientists glue these radio tags onto the monarch butterfly’s thorax. Was solar their best choice, I wonder?

BlūMorpho produces repetitive detections as the butterfly travels in areas that have receivers. Compatible smartphones, Bluetooth-enabled devices, and wildlife tracking equipment, such as Motus stations, can pick up those signals. Project Monarch’s app allows smartphones to function as mobile wildlife receivers.

This means even the public can participate. They would need to download the app, enable Bluetooth and location services, and take their phone with them while outdoors. If a smartphone is within 100 meters of a butterfly, it will record the detection. Observations like these are then uploaded to the Project Monarch network. From there, participants can see the butterfly and its movement on a map.

So far, this project has already produced results that would be difficult to collect with standard tagging. During Fall 2025, researchers deployed over 400 BlūMorpho transmitters across southern Canada and the northern U.S. Individual butterflies were followed via thousands of miles of detections toward Mexico. In Ontario, where the first deployments took place, high-resolution recordings tracked monarchs crossing Lake Erie.

In March 2026, Project Monarch started documenting a bigger achievement. 28 monarchs that were tagged in the fall arrived at Mexican overwintering latitudes. Meanwhile, two other monarchs were tracked heading back north. A butterfly called XSTI009 flew from Oklahoma to Mexican overwintering sites. It then traveled back to Texas, making it the first tracking of an individual butterfly that completed the southbound trip to Mexico before the return journey began. This dataset exceeded 32,000 detections.

Researchers could use this data to identify crucial stopover habitats, understand how weather affects migration, predict survival rates, and determine the landscapes that monarchs rely on while traveling.