The monarch butterfly's multi-generational migration is a marvel of the natural world. Scientists have long hypothesized that monarchs use an internal magnetic compass for long-distance navigation, a theory bolstered by the discovery of light-sensitive magnetoreceptors in their antennae. In a key experiment, researchers coated monarch antennae with black paint, blocking all light; these butterflies subsequently showed no directional preference in a magnetic field, unlike the unaltered control group. This indicates the antennae are essential for interpreting geomagnetic information, allowing the butterflies to maintain their course over thousands of miles.