A swarm of colourful butterflies

Painted lady (Cynthia cardui)

Throughout most of last week several birdwatchers and other naturalists, in addition to migrating birds, were observing the migration of painted ladies, small whites and other butterflies. Hundreds of thousands probably passed over the Maltese in a few days.

Butterflies are known to migrate in spring from North Africa to Europe. There is no regular pattern and the number varies from one year to the other.

On Monday six painted ladies were recorded on the islet of Filfla. More were seen on Tuesday and Wednesday. Little were those noting these migrating butterflies to know that these few migrants were just the advance party of an amazing migration of painted ladies and other species. By Thursday the numbers being observed had increased considerably. 

Hundreds were observed in many areas and thousands were observed particularly along the Magħtab-Baħar iċ-Ċagħaq Coast Road, all flying out to sea in a northerly direction. At San Anton Gardens in Attard, hundreds were drinking nectar from  the orange flowers of the lantana bushes. The largest numbers were observed at the Għadira Nature Reserve. 

One of the wardens made several counts. A typical count was 1,100 butterflies in fifteen minutes. He estimated that about 25,000 painted ladies passed through the reserve during the morning. On Friday even more were counted. Between 30,000 and 40,000 were observed about 25,000 near the Red Tower, slightly to north of the reserve.

A birdwatcher tried to make some counts at different points along the Baħar iċ-Ċagħaq Road. He placed his binocular in a fixed point and counted the number of butterflies flying out at sea heading north and counted between 80 and 120 painted ladies passing by every minute.

By Saturday the number of migrating butterflies went down to a few tens but many remained in the countryside and gardens in built up areas feeding on flowers.

The painted lady is one of the most widely distributed of all butterflies. It is found on every continent during some part of the year except in South America, where the species is rare or absent.

This species seems best adapted to dry and open land and is unable to survive freezing temperatures in any of its stages. The painted lady does not overwinter north of the Mediterranean. Each spring there is an annual migration of butterflies from more southern regions of Africa, sometimes in small, sometimes in massive numbers.

The causes of sporadic population explosions and associated migrations have intrigued biologists since the beginning of scientific research. Few biologists work solely on migration studies. Still fewer are fortunate to be in an area where a migration is taking place.

Last week’s butterfly migration was not the first and will not be the last to take place but it was one of the most spectacular that took place in the past few decades. It is not known why so many butterflies migrated but it is probably a result of favourable weather during the breeding season which resulted in more butterflies reaching adulthood. It could also be the result of climate change which presently is providing the right conditions for butterflies to reproduce. Scientific studies in the breeding and wintering areas could provide the answer to some of these questions and partially solve the mystery of migrating butterflies. 

This article was published in The Times on 27 May 2009.