A 60-milligram solar-powered radio tag has produced the first end-to-end track of an individual monarch butterfly flying south to Mexico and back north again. The dataset behind that single insect, a butterfly coded XSTI009, exceeded 32,000 detections collected over the 2025–2026 migration season.

The tag, called BlūMorpho and built by Cellular Tracking Technologies, carries no battery. A small solar cell powers a digitally coded transmitter that broadcasts an identification signal on the 2.4-GHz band — the same spectrum Bluetooth uses. Researchers glue the device to the monarch's thorax. At 60 mg, it is light enough for an insect that flies up to 3,000 miles from southern Canada and the northern U.S. to mountain forests in central Mexico each autumn.

How does the tracking network work?

BlūMorpho tags emit repetitive detections wherever receivers exist. Three classes of hardware can pick up the signal:

• Compatible smartphones running the Project Monarch app
• Bluetooth-enabled devices
• Wildlife tracking equipment such as Motus stations

The smartphone component is what turns the project into a crowd-sourced network. Participants download the app, enable Bluetooth and location services, and carry their phone outdoors. If a phone comes within 100 meters of a tagged butterfly, it records the detection. The app uploads each observation to the Project Monarch network, and participants can watch individual butterflies move across a map.

What did the 2025 season deliver?

Researchers deployed more than 400 BlūMorpho transmitters across southern Canada and the northern U.S. during Fall 2025. Individual butterflies were then followed through thousands of miles of detections toward Mexico. In Ontario, where the first deployments took place, high-resolution recordings captured monarchs crossing Lake Erie — detail that conventional wing tags and broad population counts, the standard tools scientists have relied on, cannot provide.

By March 2026, Project Monarch documented a bigger milestone: 28 monarchs tagged in the fall arrived at Mexican overwintering latitudes. Two others were tracked heading back north. One of them, XSTI009, flew from Oklahoma to the Mexican overwintering sites and then returned to Texas. That round trip makes it the first documented case of an individual butterfly completing the southbound migration before the return journey began.

Why does the dataset matter?

The detection stream gives researchers material that standard tagging methods struggle to produce. According to the project, scientists can use the data to:

• Identify crucial stopover habitats along the migration corridor
• Understand how weather affects migration
• Predict survival rates
• Determine which landscapes monarchs rely on while traveling

What are the engineering trade-offs?

The design hinges on the power budget. A battery small enough for a monarch would limit tag lifetime to a single season at best, while the solar cell lets the transmitter keep emitting through the full round trip — the mechanism that made the XSTI009 track possible. The cost is coverage: a 2.4-GHz transmitter with milligrams of energy harvesting has a short range, which is why the project leans on dense receiver coverage from smartphones rather than dedicated infrastructure alone.

The Fall 2026 deployment will show whether the 28-arrival result and the first complete round-trip track scale up, as the tag-and-apple-phone network grows and more of the public carries receivers into the migration corridor.