Butterfly Brains Could Show Us Secrets of Magnetic Navigation

Monarch butterflies may hold the key to one of biology's biggest unsolved puzzles: how animals tap into Earth's magnetic field to find their way. In Texas, neurobiologist Robin Grob is performing microsurgery on monarchs, sliding hair-thin electrodes into their brains, then tethering them in an outdoor flight simulator that can alter magnetic fields. The goal is to catch neurons in the act of responding to magnetism as the insects attempt their usual southwest migration, per the New York Times. It's a delicate, trial-and-error process: the butterflies must survive surgery, behave as if they're truly migrating, and produce readable signals from just a handful of neurons in a brain with roughly 100 million.

Scientists have long known that monarchs use the sun and polarized light to navigate thousands of miles from Canada to Mexico, but the existence and mechanics of a "magnetic sense" in insects remain disputed. Some researchers, including German biologist Henrik Mouritsen, say their experiments show no magnetic compass in monarchs. Others argue the opposite and are closing in on the molecular and genetic machinery that might underlie such a sense. Work led by Texas A&M chronobiologist Christine Merlin has identified a gene, CRY1, as essential for monarchs' magnetic response, and suggests the sensors likely involve the antennae and eyes. Her team now uses CRISPR to disable specific genes and see which ones might allow for magnetic navigation.

The research could reach beyond butterflies. If scientists can pinpoint the molecules and neural circuits that let monarchs detect magnetic fields, it could clarify how other migrants—from turtles to birds, and possibly humans—orient over long distances. It might also inform new navigation technologies that function without satellites, using Earth's magnetic field as a constant reference. For now, Grob and collaborators are pursuing the problem from both ends: Merlin's group hunts for the sensors and genes; Grob and colleague Basil el Jundi record how the brain processes whatever those sensors detect. They hope this work will ultimately reveal how life reads a map that's invisible.