Long-dis­tance mi­grants

Painted ladies are among our most im­pres­sive mi­grants, says Ben Hoare.

BBC Wildlife Magazine - - Contents -

Why we have but­ter­fly in­va­sions Plus Three seaweeds for you to spot

pot a painted lady this Au­gust and you’re wit­ness­ing a tiny part of a mam­moth multi-gen­er­a­tional re­lay. Last win­ter painted ladies laid their eggs in the southern desert fringes of North Africa. Th­ese de­vel­oped into adults that then flew to the Mediter­ranean in March and early April, and in mid-May their off­spring again mi­grated north – reach­ing North­ern Europe, in­clud­ing Bri­tain and Ire­land. At the end of sum­mer, their prog­eny will in turn depart south en masse to restart the cy­cle in Africa.

“The painted lady is hard-wired to mi­grate,” ex­plains Richard Fox of But­ter­fly Con­ser­va­tion. “It’s not hardy, so can’t sur­vive win­ters in North­ern or Cen­tral Europe by hi­ber­nat­ing. In­stead it has to fly south. And at any time of year some­where in its range there will be adults lay­ing fresh eggs.”

Painted ladies ar­rive in Bri­tain and Ire­land an­nu­ally, but num­bers vary enor­mously. The last huge in­fluxes were in 2009 and 1996. Ex­perts be­gan pre­dict­ing that 2015 would be an­other bumper year when sight­ings around the Mediter­ranean surged this spring – but the hoped-for del­uge failed to ma­te­ri­alise. “We still don’t fully understand what fac­tors drive the pop­u­la­tion cy­cle,” Fox ad­mits.

But one en­dur­ing mystery has been solved – how painted ladies man­age their epic south­bound jour­ney. In Septem­ber 2009 the spe­cialised en­to­mo­log­i­cal radar at Rotham­sted re­search sta­tion in Hert­ford­shire tracked swarms of them head­ing south at an al­ti­tude of 400–500m. “It seems they can sam­ple the speed and di­rec­tion of air­flow at dif­fer­ent heights to se­lect the best tail­wind,” says Fox.

Painted ladies love the nec­tar of this­tles, bud­dleia, ragwort and knap­weed, so keep an eye out this Au­gust.

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