WHAT WE HAVE IN COMMON WITH MONARCH BUTTERFLIES
You've probably heard of the spectacular migrations of hundreds of millions of monarch butterflies, which home in on one small region of Mexico for the winter then return as far north as Canada in a flight of thousands of miles that takes more than one generation. Clearly the insects have an inherited "map" of where to go, but what compass do they use?
It seems they have at least two compasses. One is a "time-compensated sun compass," located in their antennae, which calculates bearings from the angle of the sun corrected for the time of day.
But butterflies can also use the Earth's magnetic field to navigate. The butterfly antennae contain a protein molecule called cryptochrome, which can apparently act as a magnetic compass when exposed to blue or violet light. Human beings and other mammals also have a cryptochrome in their retinas, albeit in slightly different form, but until recently it was thought not to have magnetic directional properties.
Recently Dr. Steven M. Reppert of the University of Massachusetts Medical School and his colleagues took the human version of the gene that's the recipe for cryptochrome and genetically engineered it into flies, replacing the flies' own version. They then showed that, presented with two routes in a maze, the flies could choose a magnetic direction they had been trained to associate with a sugar reward, and they did so just as well with the "human" cryptochrome as with their own.
If it is at least possible to use our cryptochrome molecules to sense direction from the Earth's magnetic field, do we?
