Migrating animals are always impressive to watch. The ability to cover huge areas of land in massive groups can be a beneficial strategy for many animals; whether birds, mammals or shoals of fish. Yet even more impressive than migrations by groups of individuals are those that take place over several generations. In the case of the Painted Lady butterfly a 9000-mile round trip, from the tropics of Africa to the Arctic circle, takes place over six generations. Each butterfly is following the migration path, not of its parents, but of its great-great-great-great-grandparents.
Until fairly recently, it wasn't known exactly how these butterflies migrated. They appeared in the UK around spring-time and then promptly vanished in the autumn. In order to track them a project was set up in 2009, involving systematic surveys, observation through citizen science projects, and the use of high altitude insect-monitoring radars.
What they found was that when the Painted Lady migrated back down south, the butterflies travel at incredibly high altitudes, up to 500m up. By using favourable winds, they can reach speeds of up to 30mph, which for a butterfly is fairly zooming along. They'd never been seen previously because people weren't monitoring butterflies at such high altitudes. Butterflies such as Red Admirals were seen and recorded travelling southwards, but the Painted Ladies were so high up they were able to vanish unnoticed.
Painted Ladies aren't the only butterflies that carry out these multi-generational migrations. The most famous migrating butterflies are probably the Monarch butterflies in America, which takes four generations to migrate from Canada and Mexico. Once again, these butterflies aren't using memories, or even passed on knowledge of the migration routes to find their way. Each generation must work it out alone with the help of genetics and instinct.
I find these multi-generational migrations truly fascinating; the idea that these tiny little creatures, with brains approximately the size of a pin-head, are capible of following migratory patterns laid down many generations ago. It's like a butterfly generation-spaceship, with each individual seeing only a small fraction of the distance and scenery of the full journey.
Brocken Inaglory images
Reference: Stefanescu, C., Páramo, F., Åkesson, S., Alarcón, M., Ávila, A., Brereton, T., Carnicer, J., Cassar, L. F., Fox, R., Heliölä, J., Hill, J. K., Hirneisen, N., Kjellén, N., Kühn, E., Kuussaari, M., Leskinen, M., Liechti, F., Musche, M., Regan, E. C., Reynolds, D. R., Roy, D. B., Ryrholm, N., Schmaljohann, H., Settele, J., Thomas, C. D., van Swaay, C. and Chapman, J. W. (2013), Multi-generational long-distance migration of insects: studying the painted lady butterfly in the Western Palaearctic. Ecography, 36: 474–486. doi: 10.1111/j.1600-0587.2012.07738.x