Researchers track animal movements through tags on their limbs, wings, and shells, but how do you track a creature that weighs less than a gram? To build a device tiny and light enough for a monarch butterfly, designers had to make the smallest wildlife tracking device on the planet.
A tiny transmitter for butterflies designed by the New Jersey-based Cellular Tracking Technologies (CTT) is called the BlūMorpho. It’s just three-and-a-half centimeters (1.4 inches) long, weighs about as much as a grain of rice, and works without a battery.
CTT manufactures devices for wildlife telemetry, or tracking the movements and migration patterns of wild animals. After bringing its manufacturing in-house during the COVID-19 pandemic, it was able to make minuscule parts on its own.
“We’ve been a telemetry company since 2007, and we work primarily with birds, so everything is about saving weight,” David La Puma, CTT’s vice president of global market development, tells Fast Company. Designing for a butterfly’s weight, however, was “an extreme constraint,” La Puma says, adding that designing and manufacturing the product took significant investment.
Instead of a battery, the tracker uses a super tiny solar panel, smaller than the torch on the back of a dime, that’s located at the top of the transmitter. Most of the device is a skinny antenna that runs down the body of the model and transmits information to fixed receiver stations.
In spring 2025, 30 butterflies equipped with BlūMorpho were released from Ontario, Canada, to track their migration south as part of a research collaboration, Project Monarch. More than 400 butterflies were tagged and tracked last fall, a number that grew to about 1,500 this year, and the goal is to reach more than 2,000 butterflies after tagging over the winter. Being able to gain insights could be helpful at a time when butterflies are in decline due to threats like climate change and habitat loss.
At the Vermont Center for Ecostudies, conservationists are using the trackers to determine how many Vermont Monarchs make it south to Mexico, and if they don’t, where the threats and bottlenecks are along the way. They’re also using the trackers to determine whether the butterflies have a better chance of surviving if they migrate earlier in the year.
Staff at the center are able to put the trackers on the butterflies after placing the butterflies in a fridge for about 20 minutes to slow them down. From there, a butterfly is placed on a spreading board with its wings spread under small weights to keep them from moving. The transmitter is then glued to the butterfly’s thorax with nontoxic eyelash glue that dries in 15 minutes. After a short time in a temporary cage to make sure the tracker is working, the butterfly is released into the wild.
“With these transmitters, it’s the first time we can actually see the movements of individuals. We’ve never been able to do that before,” says Desirée Narango, a conservation scientist at the center.
The center’s staff have found that butterflies take various migratory paths across a broad geographic area. They’ve been able to see how fast they fly, how far, and how long their sustained flight is, as well as the approximate location they are stopping to find nectar and refuel. That could be a small pollinator garden in a backyard or school, or near threats like roadways and pesticides.
“Being able to see just how important these small patches of habitat are for their migratory journeys has been eye opening,” she says, and they’re now talking about potentially using these transmitters on dragonflies or bumblebees, too.
“There are a number of migratory insects here in North America that we know almost nothing about,” she says. “This technology will really revolutionize our understanding of migratory behavior.”
