I have a little personal history with monarch butterflies: my grandmother used to catch them with my sister and me with a huge butterfly net, then kill them with Raid and put them in flower arrangements. So I rather like the little creatures, and am disappointed that their Mexican fir grove wintering grounds are being destroyed by stupid Mexican workers who only care about money, though what else can you expect with those people.
Anyway, scientists have wondered for years how monarch butterflies are able to find their way back to those forests. Even if you take a migrating monarch and move it to a completely different part of the country, they will still figure out the correct direction to travel. Now we have a big piece of the puzzle.
In a new article in Science, researchers have found that the monarchs contain some type of circadian "clock" in their antennae (independent of their brain) that they use to track the sun's movement, and then determine the correct direction based off of that information.
From a summary article here:
The researchers next covered the antennae in black paint, effectively blocking light sensing by the antennal clocks. Those butterflies homed in on an incorrectly fixed direction: the insect's brain could sense light but couldn't adjust the timing of the sun's movement across the sky in order to steer towards the proper destination. However, when the team used clear paint—which did not alter antennal light input—the butterflies accurately established the southerly flight orientation, indicating that the antenna's reading of light is key to navigation.
Cool, huh? I wish I had antennae. And wings.