A species of butterfly found in Sub-Saharan Africa is able to migrate thousands of miles to Europe, crossing the Saharan Desert, in years when weather conditions are favorable, scientists have found. The striking Painted Lady (Vanessa cardui) butterfly has been shown for the first time to be capable of making the 12,000-14,000 km (7,456-8,700 mile) round trip--the longest insect migration known so far--in greater numbers, when wetter conditions in the desert help the plants on which it lays eggs. The international research team's findings increase understanding of how insects, including pollinators, pests, and the diseases they carry could spread between continents in future as climate change alters seasonal conditions. Professor Tom Oliver, PhD, an ecologist at the University of Reading (UK) and co-author of the study, said: "We know that the number of Painted Lady butterflies in Europe varies wildly, sometimes with 100 times more from one year to the next. However, the conditions that caused this were unknown, and the suggestion the butterflies could cross the Sahara desert and oceans to reach Europe was not proven.”