The story of the Painted Lady Butterfly Vanessa cardui is full of surprises, and some facts about its life have only recently been discovered. We don’t see them every year on the reserve at St Nicholas Fields, but when they do appear, as they did in 2013, 2015 and 2016, they charm us with their beauty.
Painted Ladies are migrants from North Africa. Some years are ‘good’ Painted Lady years for Britain, with millions crossing the English Channel in spring, while in other years they are much scarcer. In a good year they can reach almost every corner of the British Isles: it was the only butterfly species recorded on the remote northern Scottish island group of St Kilda during the national millenium butterfly survey. In early September 2015 the author of this blog saw many in the coastal regions of Galloway, SW Scotland.
2009 was the best, 2015 the 2nd best and 2016 the 3rd best Painted Lady year since the national Migration Watch began in 2008. What will 2017 bring? One or two have already been seen this year in the York area, including one by the St Nicks team that this year began monitoring wildlife at the Derwenthorpe housing development.
St Nicks should be an attractive spot for Painted Ladies. The adult butterflies tend to choose open areas with plenty of Thistles and Knapweed in flower to provide nectar to replenish reserves after the migrant journey and bring them into breeding condition. Another favourite nectar plant is buddleia. At St Nicks we have some good open spaces, and lots of Thistles, Knapweed and Buddleia – so if you are a painted lady what’s not to like?
Females can produce 200 eggs in a season, laid singly on Thistle plants. The dark spiky larva creates a silk tent for itself on the underside of a leaf, where it feeds. As it grows it makes larger tents until it is ready for pupation. The whole life-cycle can take as little a month to complete, newly-emerged adults soon mating to start another brood. There can be several broods in a good summer.
Then what happens? Painted Ladies can’t survive the British winter, and it was once thought that the entire British Isles population died out. Wrong! Radar studies have shown that painted ladies migrate back south in even greater numbers than their earlier arrivals. In 2009 11 million individuals were logged entering southern England during May and June, followed by 26 million returning between August and October. The reason why this was not known by visual observation is because they fly at an average altitude of 500 metres, some reaching 1km.
Flying with favourable winds in spring or autumn they achieve migration speeds of 30 mph, more than twice their capability under their own steam. Breeders inside the Arctic Circle can make an annual round trip from North Africa of 9,000 miles, almost double the distance of the famous Monarch butterfly migration in North America.
Further discoveries have been made. While the earliest migrants might possibly make it in one hop from Morocco to Devon, most of those arriving here are the children, grandchildren or even great-grandchildren of the butterflies which started out a few months before. Being rapid breeders, Painted Lady migration is like a relay race, and up to six successive generations can be involved in one 9,000 mile round trip from spring to autumn.
A short BBC video explaining this can be seen here:
Maybe this astonishing story will make you want to approach a Painted Lady butterfly with a sense of awe and wonder.
All photos were taken at St Nicks.