Scientists say they’ve solved the monarch butterfly migration mystery

It’s the only insect that migrates thousands of miles, from as far north as Canada to the northern parts of South America. But the monarch butterfly migration has always been a mystery.

Until now.

Researchers from the University of Washington say they’ve figured out how the colorful member of the Nymphalidae family manages this improbable feat. The Monarch, they explain, uses an internal “sun compass” to maximize their months long journey.

The researchers created a model for a time-compensated sun compass that is used by monarch butterflies to chart their flight in a southwest direction. They found the insects use the sun exclusively as a guide to optimize the bulk of their flying during midday, which is the most advantageous time for migratory flight.

“We identified that the input cues depend entirely on the Sun,” lead researcher Professor Eli Shlizerman told the BBC. “One is the horizontal position of the Sun and the other is keeping the time of day. This gives [the monarchs] an internal Sun compass for travelling southerly throughout the day.”

Shlizerman says the study’s findings may lead to advances in the field of robotics because it demonstrates that the monarch migration can be understood in terms of cellular circuitry. He says robots today are “far cruder” than the simplest nervous system.

“For me this is very exciting – it shows how a behaviour is produced by the integration of signals,” he said. “We can take these concepts to produce robotic versions of these systems – something [that is] powered by and that navigates by the Sun.”
The study was published in the journal Cell Reports.

Earlier this month, the David Suzuki Foundation launched its third annual #gotmilkweed campaign to highlight the plight of the monarch butterfly population. The foundation says planting milkweed can help bolster flagging monarch numbers because it is the only plant that the butterflies lay theor eggs on and is the primary source of food for monarch caterpillars.

The numbers are dire. A recent study found the Eastern migratory monarch population declined by 84 per cent between the winter of 1996-97 and the winter of 2014-15. Because it is difficult to count individual monarchs, scientists use geographic area to estimate population sizes, with the 2014-15 population figured to be about 2.8 acres in size (the population was at its lowest a year earlier in 2013-14 at 1.7 acres). The damage can happen quickly: a single snowstorm in early March of this year is estimates to have killed as many as 11-million monarchs.

The study found a “substantial chance” (somewhere between 11 and 57 per cent) of quasi-extinction of the monarch over the next two decades. Quasi-extinction marks a species population small enough that any chance of recovery is impossible.

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