A single painted lady butterfly can cross Europe and the Sahara
head hawkmoths, and the delicate vestal moth. Enthusiasts call these migratory moths, but Richard Fox of Butterfly Conservation distinguishes between insects that are simply dispersing as widely as possible after a successful breeding season, and “obligate”, or true, migrants. Most migratory moths are on a fairly fruitless dispersal. “The killer piece of evidence is that the best time of year to see migrant moths is the autumn,” says Fox. “To me as a biologist they can’t be ‘proper’ migrants because the habitat here in winter is not going to support their breeding cycle and they are unlikely to survive.” In other words, Britain is a dead-end.
insects cross continents
It seems far- fetched that
In contrast, obligate migrants build their life-cycle around migration. For British butterflies, the big challenge is to survive winters when caterpillars’ food plants don’t grow. Most do this by hibernating. But migrants such as the clouded yellow survive by moving south, to warmer climes. It was long assumed that the painted lady retreats to Morocco but scientists have recently discovered
that it also crosses the Sahara. Then, when it gets too hot for the sub- Saharan African generation, they move north again. The painted lady migration route can span up to 7,500 miles but this may be via three or more quickly-reproducing generations. Such insights have been gathered using new forensic techniques, analysing chemicals found in painted lady wings to discover where individuals grew up as caterpillars.
Until the 2009 painted lady invasion, it was unclear if Britain was a dead-end for the species. People observed painted ladies arriving but never saw them depart and their offspring couldn’t survive winter.
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