How Monarch Butterflies Migrate Thousands of Miles: It's All in the Shape of the Wings

Millions of monarch butterflies make a spectacular journey each year, traveling thousands of miles from the eastern parts of North America to reach their overwintering grounds in Mexico. Now, scientists have found out how these butterflies are so successful at traveling these vast distances. It turns out that it all has to do with the shape of their wings.

In this case, the scientists analyzed how the size, shape and color of wings differed among a collection of migrant butterflies. Although previous studies have looked at how much wing sized varied within a migratory season, they didn't account for specific measures of wing shape and color.

The researchers captured monarch butterflies as they migrated through northern Georgia in the fall of 2010. Each monarch was then scanned with a flat bed scanner in order to produce a digital copy of their wings. The researchers then used computer software in order to measure the features of the wings.

So what did they find? It turns out that early migrants not only have larger wings, but the wings are also more elongated. Both of these features promote long-distance migration. In addition, these migrants had redder wing colors, which correlated to previous work that showed that butterflies with redder wings tend to fly farther.

That's not all that the researchers found, either. The scientists noted that monarch butterflies that migrated the latest were more likely to be small, have less elongated and paler wings. This suggests that these features slow the migratory pace. In fact, it's likely that stragglers fell behind and may have even failed to reach their overwintering destination.

The findings reveal the optimal wing characteristics that these monarch butterflies need to carry out their migration. As monarch butterfly populations decline due to climate changes, it's more important than ever to determine what these butterflies need in order to be successful.

The findings are published in the journal Animal Migration.