A painted lady butterfly in Morocco
(Orio Massana)
The ‘Painted Lady Butterflys’ are true cosmopolitans! Known for making extremely long migrations, these tiny insects fly to the cooler north in summer and warmer south in winter. In search of an “eternal source” they undertake arduous journeys of several thousand kilometers every year. Aerial photographs have often indicated mass movement of these butterflies, covering almost the entire lengths of Africa, Asia, Europe, and North America.
Researchers from China, Spain, Great Britain and the Netherlands have now successfully followed the longest known insect migration route in a 22-year collaborative study. The study provides one of the first empirical evidence to prove that Painted Lady Butterflys beat the previously held record of longest migration of monarch butterflies.
It may seem absurd that such fragile, short-lived, and weak flying beings as butterflies should make this long annual journey of 14,000 kilometers every year – but these are the wonders of nature!
Using atmospheric and climatic data and population dynamics models, the study also identifies the driving factors that help maintain large butterfly populations over such a long migration path.
The study delves into the climatic conditions that prevail along the western part of the Afro-Palearctic migratory area of these butterflies. It extends over the region between the tropical forests south of the Sahara to Fennoscandia and crosses dry and semi-arid regions of the Sahara, Sahel, Maghreb, southern Iberia, Mediterranean and the Scandinavian countries.
“We know that the number of Painted Lady butterflies in Europe fluctuates a lot, sometimes even hundreds of times from year to year. However, the conditions that caused this were unknown and the suggestion that the butterflies could cross the Sahara and oceans to reach Europe has not been proven, ”says Professor Tom H. Oliver, Ecologist at the University of Reading, Great Britain, and a co-author of the study.
Winter spring green patches in the African savannah and North Africa have been found to maintain and build large populations and to ensure a spectacular influx of painted ladies to Europe. The vegetation in these landscapes provides breeding grounds for the rearing of caterpillars and larvae and sources of nectar for adult animals. Years with comparatively higher precipitation can lead to the population size increasing up to 100 times in the following year. In addition, the butterflies use different flight strategies during this trip by staying very close to the ground to combat headwinds – blowing against their flight direction and reaching a height of about a thousand meters above the ground for optimal use of tailwind – blowing into the same direction as the flight.
“This research shows that this unlikely journey is possible and that certain climatic conditions that lead to train season have a major impact on the number it makes requires strong international collaboration,” says Prof. Oliver.
The collection of such migration data through the Butterfly Monitoring Scheme (BMS) is widespread in most of the countries experiencing such migration events. Modeling and studying these events, the patterns they reflect, and the drivers of the process can provide proxy indicators for several climate parameters and weather determinants. Long-term studies can also be helpful in gaining knowledge about the mass movements of insects and in strengthening the knowledge for the corresponding modulation of agricultural practices and the development of conservation strategies.
The study was published this month in the journal Proceedings of the National Academy of Sciences (PNAS) and is available here.
**
For weather, science and COVID-19 updates on the go, download The Weather Channel app (in the Android and iOS stores). It’s free!
