From the Toronto Star:

Researchers showed the existence of photosensitive cells in monarch butterflies' antennae, which were long thought to provide them with their sense of smell alone. These cells appear to act like a GPS as the monarchs make their fall migration.

A ‘huge surprise’ to Monarch researchers

Monarch butterflies reach out for the sun with their antennae to navigate their miraculous, pinpoint migrations to and from Mexico, a new study has discovered.

“It was a huge surprise,” says Dr. Steven Reppert, a University of Massachusetts neurobiologist and senior study author, of the finding.

“We thought we had it nailed,” he says of the previous theory – that the butterfly’s brain provided its sense of direction.

The study appears today in the journal Science.

In it, researchers showed the existence of photosensitive cells in the insects’ antennae, which were long thought to provide them with their sense of smell alone.

These cells, Reppert says, appear to act like a GPS as the monarchs make their fall migration.

Reppert happened on observations made 50 years ago by Canadian butterfly observer Fred Urquhart, who noted that the insects seem to lose their sense of direction when their antennae are removed.

“We thought, well, we’ll try this and see, and lo and behold it’s true.” Scientists clipped the antennae from a number of butterflies, or painted others with black enamel, tethered them and placed them in an outdoor flight simulator.

These butterflies would still fly in a straight line, but in all kinds of different directions, Reppert says.

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