OUT OF AFRICA (AND INTO YOUR BACK GARDEN)

A butterfly that migrates 2,000 miles? Radio 4’s Martha Kearney on the Painted Lady’s epic journey

When journalist Martha Kearney was stung by a bee in her garden, an allergic reaction nearly killed her. The presenter of Radio 4’s The World At One was rushed to hospital with a rash across her whole body and a constricted throat that threatened to choke her. But the experience opened a new chapter in her life – by turning her into a butterfly fanatic. ‘My life was current affairs and politics,’ she says, ‘now I’m addicted to the world of insects.’

Her fascination began when she was given a beehive but, following the near-fatal sting, she had to put aside her passion for bees. Instead she started to observe the butterflies that were drawn to the wildflowers she’d planted to provide nectar for honey. In particular, Martha was attracted by the Painted Ladies – brilliant orange butterflies with black wingtips and camouflaged brown undersides. What she discovered about them was astonishing.

In a TV documentary this week, Martha reveals why the Painted Ladies in her garden have flown 2,000 miles to be there as part of the longest insect migration on earth. The Great Butterfly Adventure follows them as they leave breeding sites in Morocco, soar over the Mediterranean and end up in Britain’s back gardens.

Incredibly, the hardiest are able to make the journey in one 36-hour non-stop flight, although many take much longer. Those that fly direct ascend to a height of about three-quarters of a mile above the North African sands, before prevailing windstreams catch them and whisk them north at speeds of up to 40mph. And though we expect to see Painted Ladies in our gardens during summer, the first arrivals have been spotted in January, even on New Year’s Day.

But as the butterflies only live for about three weeks, many make stopovers in Spain and France to reproduce, meaning the journey can take in several generations. So the butterflies that arrive here will often be the grandchildren of the insects that left Africa.

It’s an amazing odyssey for a creature that’s just 5cm (2in) long. Their antennae can sense the time of day and where the sun should be in the sky, adjusting their flight path accordingly.

In Morocco, Martha meets Spanish lepidopterist (or butterfly expert) Dr Constanti Stefanescu. He’s devoted his life to the study of Painted Ladies, puzzling over why they leave Morocco to roam as far north as Iceland and Norway. They can’t spend winter in northern Europe because it’s too cold – butterflies need the warmth of the sun to give them energy. He discovered that they’re forced out of Africa by parasitic wasps, which lay their eggs in caterpillar larvae. The wasp grubs grow inside the caterpillars, consuming them from the inside out. By spring, the wasps are killing up to 70 per cent of the caterpillars. If the species is to survive, it has to flee. Constanti also proved that Painted Ladies don’t just migrate north: they return south for the winter and the round trip from Africa to Iceland can be up to 9,000 miles. For the show, Martha had to master a piece of very old technology – the butterfly net. ‘There’s a knack to Martha with a Painted Lady using it,’ she says. ‘You twist your wrist once the butterfly’s in the net, to stop it escaping, and then clench your fingers around the middle of the net to keep the insect trapped. But you must be gentle – it’s easy to damage the wings with a fingertip and dislodge its scales so it can’t fly.’

Like bees, butterflies are in decline in Britain because of habitat loss. Without their staple foods, especially thistles, Painted Ladies will become a rare sight here. ‘I’m planting thistles,’ says Martha. ‘Most gardeners see them as the enemy, but they’ll look beautiful covered in butterflies.’

Two years of immunotherapy, with injections of bee venom, should mean Martha will soon be safe to return to beekeeping. But for now, her new addiction is taking up all her time. ‘On holiday on the Norfolk Broads this summer I couldn’t stop watching the butterflies,’ she says.

But she doesn’t take her net with her. That’s strictly for scientific research. And it’d be wrong to delay a Painted Lady when she’s got a 2,000-mile journey ahead of her. The Great Butterfly Adventure is on Monday at 9pm on BBC4.