A large buddleia in full flower along our street played host for at least ten days in late August to a painted lady (pictured), a migrant butterfly which usually reaches Wharfedale in small numbers each year but a species I often miss completely. With another seen during the second of my twice yearly butterfly surveys below Harewood in Lower Wharfedale, only the third year I have recorded them there in nine years of surveys, plus a number seen by our son a week before at Bempton Cliffs, I have been wondering whether a mini-invasion has been taking place.
The painted lady is the butterfly with the widest world distribution, found on every continent except South America and capable of long distance migrations, occasionally in enormous numbers.
The last mass migration to pass through Britain was in 2009 when it was estimated that about 11 million arrived. The trigger then was thought to be above average rainfall in North Africa leading to exceptional vegetation growth and an explosion in the painted lady population with millions then heading north through Europe. I have a note of nine feeding on May blossom above Thruscross Reservoir on 31st May that year with smaller numbers on each of my two Harewood surveys.
Individual painted ladies can cover 100 miles a day during migration but research has shown that the individuals reaching our shores are not the same ones which left their original African breeding grounds. At stages on the journey the butterflies mate and, after the breeding cycle is complete, it is their offspring which carry on north to repeat the process, with the migration occurring more like a relay involving up to six generations of butterflies. Certainly the painted lady on our local buddleia looked in pristine condition and may not have been on the final leg of the migration if it could locate a mate.
They seem unable to survive British winters but it is thought that, once their final breeding cycle is complete many will attempt to return south. In 2009, radar studies apparently showed an astonishing 26 million flying south in the autumn.
Another migrant butterfly with a similar life pattern is the more familiar red admiral and I had seen none until one joined the painted lady on the same buddleia. With a few peacocks and large whites feeding on the same bush it made an enticing sight after a summer when, for weeks on end, butterflies have hardly been visible.