Butterflies

Amiral Vanessa atalanta: Foto: Oskar Brattström

Just as there are migratory birds, there are several species of butterflies which fly long distances every year. While most butterflies are adapted to spend parts of the year in a dormant state as an egg, larva, or even as an adult butterfly, there are species which instead move with the seasons to avoid environments that are too warm or too cold. Capri is a good location to study this phenomenon in Europe.

One of the migratory species of butterflies, the Red Admiral, spends the winter months around the northern coasts of the Mediterranean, where the climate is mild enough to reproduce even in the winter. In the spring the new generation moves north through Europe, in exceptional cases some individuals may reach the Arctic.

When the Red Admiral reaches its summer areas, the females lay their eggs on nettles and in the late summer a new generation of butterflies hatches, and soon moves back south to spend the winter in the Mediterranean area.

Unlike birds, which live longer and make the same journey back and forth several times, each individual butterfly only travels one way, either north in the spring or south in the late summer.

Tistelfjäril Vanessa cardui: Foto: Oskar Brattström

A closely related species, the Painted Lady, has an even more impressive migration, which however is not as well charted as the Red Admiral’s. The Painted Ladies which are seen in Europe every summer fly north in the spring, just as the Red Admiral, but start their journeys south of the Mediterranean, in some cases perhaps as far away as West Africa! They spread across all of Europe, and have even been found on Iceland. But like the Red Admiral, they cannot survive the cold winters and move south in the late summer. They fly then across the Mediterranean but we do not know yet exactly how far they continue. In some years the Painted Lady is very common, but in other years hardly a single individual can be found in northern Europe. The occurrence of the Red Admiral also varies, but it is more regular.

On Capri we are investigating the migration patterns of these two species of butterfly. The Red Admiral is on Capri during the coldest six months of the year, and we study the differences between the butterflies which arrive from the north in the autumn and those who later fly north in the spring.

We have been able to show that those hatch in the spring and fly north are clearly smaller than those who arrive in the autumn. But there are no differences in how much fat they take on as fuel for flying.

The Painted Lady is basically only on Capri as they fly through in the spring and autumn during their passage across the Mediterranean. On some spring days, often the same days when there are many migratory birds, there can be enormous numbers of Painted Ladies, who however continue north more or less immediately. In the autumn their offspring come through on their way south, but in not in the same numbers as during the spring. Possibly this is because they follow the coast of Italy south, instead of heading towards Capri?

Oskar Brattström, doctoral student, Department of Animal Ecology, University of Lund