Mystery decoding: How butterflies navigate their way

The magnetic compass is migration's final mystery, and monarchs may hold the key

- ALEXA ROBLES-GIL

IN A STORAGE shed beneath a cloudless Texas sky in November, Robin Grob performed open brain surgery on a monarch butterfly.

Slips of tape pinned the butterfly beneath a microscope, its black-and-orange wings held open as Grob, a neurobiologist at the Norwegian University of Science and Technology, inserted a tetrode — four hair-thin electrodes — into a tiny yellowish brain. He sealed the head with silicone to keep the electrodes from shifting. As the butterfly struggled, he murmured gently, “Calm down. Stop moving.”

The most difficult part came next: transporting the butterfly outdoors to a flight simulator — a metal cylinder where it would be tethered and allowed to fly through a controlled magnetic field. One jolt could undo hours of work. But if the electrodes stayed in place, Grob could capture the precise moment the butterfly’s brain sensed the magnetic field that helps guide monarchs across a continent.