Annual Review '25-26: Tiny tags, big migration

At KU Libraries, a project weighing just six milligrams is helped researchers follow one of nature’s most extraordinary journeys.

Inside the Makerspace on the second floor of Anschutz Library, students and staff 3D-printed replica radio tags that mimic the devices attached to monarch butterflies. The practice tags are small, precise and inexpensive, a low-risk stand-in for real tracking technology that costs about $75 per tag.

The collaboration began when doctoral student Cailin Kessen approached the Makerspace with a challenge for Monarch Watch: recreate a tracking tag from rough measurements and photos, then make it light enough for a butterfly to carry.

Makerspace Coordinator Matt Bristow started from scratch, printing, weighing, and refining prototype after prototype until the sixth version hit the target: a replica matching the real tag’s shape, size, and six-milligram weight.

That precision matters. The real tags use solar power and Bluetooth to ping nearby cellphones, sending location data to an app that tracks monarch migration in real time. Before attaching them to live butterflies, Kessen’s team can now test adhesives and techniques with lookalikes that cost only pennies to print.

For KU Libraries, the project shows how a free creative resource can move research forward in unexpected ways — turning a rough idea, a few photos and a 3D printer into a tool for studying a migration that spans North America to Mexico.

This story first appeared in KU Libraries 2025-26 Annual Review, a publication that reviews accomplishments of the past year and provides a glimpse of priorities moving forward. See this story and discover more in the full issue via the downloadable pdf.