Monarch butterflies are famous for their long-distance migration from North America to Mexico every fall.
But how do they manage to fly so far and so efficiently? A new study suggests that the answer may lie in their distinctive wing coloration, especially the white spots around the black edges.
According to the study, published in PLOS ONE, monarchs with more white spots on their wings are more successful at reaching their wintering destination, as per Phys.org.
The researchers analyzed nearly 400 wild monarch wings collected at different stages of their journey, measuring their color proportions.
They found that the successful migrant monarchs had about 3% less black and 3% more white on their wings.
The authors believed that the white spots may alter the airflow patterns around the wings, improving their aerodynamics.
They also suggested that the white spots may help the butterflies capitalize on solar energy, since they are exposed to more sunlight during their migration.
The white spots may create subtle temperature differences on the wing surface, which could affect the lift and drag forces.
The researchers also compared the wing coloration of monarchs with six other butterfly species that do not migrate or migrate only partially
They found that monarchs had significantly larger white spots than their nonmigratory cousins. The only other species that came close to having the same proportion of white spots on its wing was its semi-migratory relative, the southern monarch.
How climate change and other threats may affect monarchs' migration
The study's findings have implications for how climate change may affect the monarchs' migration in the future, as per ThoughtCo.
As temperatures continue to rise and alter the solar radiation reaching Earth's surface, monarchs may have to adapt to maintain their aerial efficiency.
The researchers warned that with greater solar intensity, some of that efficiency could go away, hindering the species' fall migration to Mexico.
Climate change is not the only threat that monarchs face along their journey. They also have to contend with habitat loss, pesticide use, diseases and parasites, and human activities that disrupt their migration.
Here are some of the main challenges that monarchs encounter:
Habitat loss: Monarchs depend on milkweed plants to lay their eggs and feed their caterpillars. However, milkweed populations have declined drastically in North America due to agricultural expansion, urbanization, and herbicide use. Roundup-resistant crops, for example, allow farmers to spray their fields with herbicides that kill milkweed and other weeds without harming their crops. Monarchs also need nectar plants to fuel their flight, but these have also become scarce in many areas.
Pesticide use: Monarchs are vulnerable to insecticides that are applied to crops or sprayed aerially to control mosquitoes and other pests. Some insecticides, such as permethrin and Bt (Bacillus thuringiensis), can kill monarch caterpillars if they come in contact with them or ingest them through milkweed leaves. Other insecticides, such as neonicotinoids, can impair monarchs' ability to navigate and reproduce.
Diseases and parasites: Monarchs can suffer from various infections and infestations that can reduce their survival and reproduction. One of the most common and harmful parasites is Ophryocystis elektroscirrha (OE), a protozoan that infects monarchs during their larval stage and causes deformities and weakness in adults. OE can spread rapidly among dense populations of monarchs, such as those in overwintering sites or breeding grounds.
Human activities: Monarchs face many dangers from human activities that disturb or destroy their habitats or interfere with their migration. For example, logging and mining in Mexico threaten the integrity of the overwintering forests. Avocado farming in Michoacán also contributes to deforestation and water scarcity in the region. Roadside maintenance can eliminate milkweed and nectar plants along migratory corridors. Illegal hunting and collection of monarchs can also deplete their numbers.
Monarchs are not only beautiful and fascinating creatures, but also important pollinators and indicators of environmental health.
Understanding how their wing coloration helps them migrate is one step towards ensuring their survival and protection.
