A 60-Milligram Solar Tag Lets Phones Help Track Butterfly Migration

An ordinary phone can become a passing witness to a butterfly migration. Solar-powered radio tags are light enough to ride on monarchs, and nearby receivers can log their presence. The Associated Press reported on November 3 that nearly 1,750 monarchs had been fitted with solar tags this year. This is an expanding field deployment, not the debut of a newly invented tracker.

The BlūMorpho transmitter, developed by Cellular Tracking Technologies, weighs 60 milligrams, or 0.06 grams. Monarch Joint Venture says more than 400 monarchs carried tags in 2025. The larger effort now gives researchers more individual journeys to compare, rather than only the places where butterflies began and ended their trips.

Older sticker tags work like numbered name badges: somebody has to find the butterfly again and report it. Radio tags instead announce themselves to nearby receivers. There is no battery to carry; the transmitter relies on sunlight. For migration research, the change is from waiting for someone to recover a label to collecting a sequence of encounters along the way.

Phones are part of that receiving network. NH Audubon explains that people using the Project Monarch Science app can contribute detections when a tagged butterfly passes nearby. Think of those phones as roadside check-in points, not satellites following every wingbeat. A place without receivers can leave a gap, even when a butterfly travels through it successfully.

The Canadian Wildlife Federation reported November 4 that tagged monarchs from Prince Edward County crossed Lake Ontario into New York, bypassing the presumed main corridor at Point Pelee.

Another journey illustrates that variety. Monarch Joint Venture's October 4 account followed a butterfly called KIM60 from Minnesota west into South Dakota, through Nebraska and Colorado, and onward to Texas. Those are dated observations, not a claim about where that insect is today. They show why connecting individual detections can be more informative than marking a single arrow south on a map.

The Canadian Wildlife Federation cautions that butterflies must be selected for tagging by trained, permitted handlers. Its study of flight and behavior effects was still under review. Small does not mean consequence-free.

The practical aim is to identify feeding and resting habitat more precisely. A volunteer supplies one encounter; researchers combine many encounters to understand a journey and guide conservation. Better tracking can help decide where restoration matters. It cannot, by itself, preserve the places that the butterflies need.

Reporting and project update dates: November 3–4, 2026. The KIM60 account is dated October 4.