Monarch butterflies use a natural magnetic compass to navigate in their annual migrations, based on a new study. Millions of these insects make their way, more than 2,000 miles, from the eastern United States to a group of fir trees, found in central Mexico.
Researchers previously understood Monarchs used the sun to help guide them in their journeys. Biologists recorded the distinctive creatures navigating on cloudy days as well, suggesting they were not dependent on seeing the sun. This suggested a possible ability to detect the magnetic field of the Earth. Some species of birds and other migratory animals have been shown to possess a similar ability to align along the planetary magnetic field.
Steven Reppert of the UMass Medical School (UMMS) and Robert Gegear from Worcester Polytechnic Institute (WPI) headed the discovery that found the navigational ability of the insects.
The team tethered butterflies, and let them fly, for at least five minutes, in a "flight simulator" which allowed investigators to create and modify a magnetic field. When magnetic fields were altered, monarchs altered their direction accordingly.
Monarch butterflies were also shown to be sensitive to certain wavelengths of ultraviolet light. When these were blocked during tests, the insects flew in circles. Investigation of the mechanism behind the ability showed the magnetic field is likely detected in the antennae of the butterfly.
Many biologists are concerned about the threat climate change and the loss of milkweed habitat are having on Monarch butterfly populations.
"A new vulnerability to now consider is the potential disruption of the magnetic compass in the monarchs by human-induced electromagnetic noise, which can also affect geomagnetic orientation in migratory birds," Reppert said.
Earth's magnetic field changes position over the course of thousands of years. Occasionally, poles completely flip, reversing the polarity of the field our home planet. Movement of the magnetic poles is accelerating, and magnetic forces are becoming weaker over the last two centuries. Some researchers believe these changes could push the field toward its next reversal. Such an occurrence would play havoc with the butterflies, as well as global electronic systems.
"This new study shows that monarchs do, in fact, use a sophisticated magnetic inclination compass system for navigation similar to that used by much larger-brained migratory vertebrates such as birds and sea turtles. This is likely a back-up compass for the butterflies, so they can continue to fly in the right direction even on days when they can't see the sun," Gegear said.
Investigation of monarch butterflies and a possible ability to use the Earth's magnetic field to navigate was published in the journal Nature Communications.
