A leopard may not be able to change its spots but new research shows that butterflies can, evolving to survive longer migrations.
Butterflies with more white spots on their wings can survive longer migrations, according to scientists. A study conducted by ecologists at the University of Georgia, Athens (UGA) focused on monarch butterflies and found that evolution favours spottier specimens.
Monarchs travel several thousand miles every year to reach their wintering destination. It is not yet clear exactly how the spots aid their migration, but the authors speculate that they change airflow patterns around the butterflies’ wings.
“Monarch butterflies are able to fly incredible distances and this research shows that their ability may be more than just a product of the physical structure of their wings and muscles,” entomologist and broadcaster Adam Hart, who was not involved in the study, told BBC Science Focus.
“Dark and light-coloured spots on their wings heat up in the Sun differently, and this could cause a pattern of tiny eddies and airflow around the wings that might help the butterflies reduce drag. It is early days, but similar effects have been found in birds.”
Lead author of the study Andy Davis, an assistant researcher in UGA’s Odum School of Ecology, said: “We actually went into this thinking that monarchs with more dark wings would be more successful at migrating because dark surfaces can improve flight efficiency. But we found the opposite.”
Each year, monarchs travel from their native homes in the northeast of the United States and southeast of Canada to south and central Mexico – almost 3,000 miles away. Researchers of the study, published in the journal PLOS ONE, analysed around 400 wild monarch wings collected at different stages along this route and measured their colour proportions.
The monarchs found at their destination had less black on their wings, with the space instead occupied by more white spots. Specifically, these survivors had three per cent less black and three per cent more white on their wings than those that didn’t make it.
The study also found that monarchs have significantly larger white spots than nonmigratory butterflies, with the semi-migratory southern monarch being the only one coming close.
The paper’s authors believe that white spots also help the monarchs to use solar energy to fly. “The amount of solar energy monarchs are receiving along their journey is extreme, especially since they fly with their wings spread open most of the time,” Davis said.
“After making this migration for thousands of years, they figured out a way to capitalize on that solar energy to improve their aerial efficiency.”
However, the authors say rising temperatures with climate change are likely to cause a new adaptation challenge to butterflies en route to Mexico, with fewer numbers of monarchs reaching their destination. Nevertheless, a stable population and population growth in the summer is a good sign for the flying insects – as long as they can reach their wintering destination.
Understanding the mechanics of the monarchs’ wings could also provide practical knowledge for aerospace engineering. “Butterflies, and insects in general, are masters of flight at small scale,” said Hart.
“Super-efficient, and often highly agile, they are the perfect models for us to learn from if we want to perfect our own micro-UAVs and flying machines.”
About our expert:
Adam Hart is an entomologist and Professor of Science Communication at the University of Gloucestershire. As well as research and teaching, he is a regular broadcaster for BBC Radio 4 and the BBC World Service. On television, Adam has co-presented several documentary series, most notably BBC4’s Planet Ant and BBC2’s Hive Alive.
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