Painted Ladies, the world travellers

I kneeled down and crept closer. The butterfly stood tiptoeing exposing its wings fully to the low afternoon sun, warming up. I was on the coastal path by the low cliff top at Spurn Head, a well known bird migration hotspot. This was my last Painted Lady of that year, 5th October 2014. The butterfly's faded colour and worn wings suggested that it was old and had been on the wing for a while, migrating. It still had a very long journey ahead.

Cosmopolitan and warmth loving

The Painted Lady is one of the most cosmopolitan butterflies, only absent from South America, Australia and the polar regions. It is cosmopolitan in more than one sense, as it is a constant traveller, moving in search of good caterpillar food sources and away of the cold. Unlike other butterflies, which have a cold-resistant stage - which can be the egg, the caterpillar or the adult - no life cycle stage of the Painted Lady can survive cold temperatures. In the UK, most sightings occur from May to September, with a strong peak in August.

This fresh individual from 25th July (Hornsea, East Yorkshire), feeding on buddleia, is likely to have been born locally.

A male Painted Lady hilltopping in the Swiss Alps (12th August 2015).

Through the desert and back

Painted Ladies migrate north in the spring to arrive as the summer starts in Europe, and they do the reverse flight in the autumn - just like many migratory birds - although the facts and routes of their migration have been only recently been pieced together. Unlike birds, migration is achieved in several generations - individual adults live for about four weeks - so it will be different individuals who carry out each leg of a migratory flight. Scientists used to think that the Northern European individuals overwintered around the Mediterranean and in North Africa, and that if any made it across the Sahara they might reach a dead end. Even a return journey from northern Europe was doubted, as migration is less obvious in the autumn, when the butterflies fly at high altitude to take advantage of tail winds, where they are out of sight. Research in the last few years has revealed that their migratory journey encompasses sub tropical Africa in a circuit of about 12,000 km. The migratory journey of the Painted Lady is actually the longest of any butterfly, with individuals being able to cover over 4000 km journeys, easily surpassing the Monarch! Gerard Talavera and Roger Vila, from the Institut de Biologia Evolutiva in Barcelona, travelled to four countries in the African Sahel (Senegal, Benin, Chad and Ethiopia), a band of savannah environments just south of the Sahara desert in October-November, just after the rainy season, with the vegetation is at its lushest. They visited tens of sites in each country in search of Painted Ladies. They found evidence of southbound migration, with worn individuals and directional movements, and local breeding. This is evidence that the European populations must actually cross the Sahara en masse during their migrations, to spend the winter months in tropical areas after the rainy season. Overall, they estimated that between six to ten generations are involved in the yearly cycle. 

Stable isotopes and the autumn migration

Is there an efficient return autumn migration in the Painted Lady? How can we find out? Scientists can fit migratory birds with miniature geolocators before migration, and these can be retrieved when the birds return to their breeding grounds, and the collected data allows to reconstruct their migratory routes and strategies. Unfortunately this is not feasible with small insects. There is, however, an alternative technique is at hand: to use stable isotopes. Stable isotopes, which have a lot of regional variation, leave permanent signatures of the natal origin of an insect in their bodies. The tissue development of a butterfly takes place in the caterpillar and pupal stage - often occurring in a single plant, and therefore reflects precisely the isotope composition of the particular place were the butterfly developed. If the adult emerging then migrates and is captured at its destination, or en route, the stable isotope composition of its wings provides a signature of where the butterfly developed. 

In a different study, Talavera and his multidisciplinary team collected specimens from around the Mediterranean from Morocco and Spain to Israel and Egypt just as they reappeared in early spring (February to April). They then analysed the stable hydrogen isotopes on samples of the butterfly wings. These were consistent with the presence of some locally born individuals but many others had a sub-Saharan origin, providing evidence for a return migration from the Sahel and subtropical Africa in spring.

Another likely migrant, this one a spring one, found in Flamborough head, 29th June 2015.

Next time you see one of these tattered Painted Ladies, spare a thought about the incredible distance that this small insect might have covered, and that it might have spend the last week or two flying across the Sahara, crossing the Mediterranean and moving through Europe in search of food for its next brood.

More information
The Vanessa cardui project. Here.

Talavera, G. & Vila, R. Discovery of mass migration and breeding of the painted lady butterfly Vanessa cardui in the Sub-Sahara: the Europe–Africa migration revisited. Biol. J. Linn. Soc. Lond. 120, 274–285 (2017).

Talavera, G., Bataille, C., Benyamini, D., Gascoigne-Pees, M. & Vila, R. Round-trip across the Sahara: Afrotropical Painted Lady butterflies recolonize the Mediterranean in early spring. Biol. Lett. 14, (2018).

Fresh Painted ladies

It has been almost four years that I haven't seen a Painted Lady, but today I had a nice surprise when I spotted one, high on the buddleia, amongst the dozen or so Peacocks that are so abundant these days. Painted Ladies are warmth-loving butterflies, unable to survive our winters, so before the cold sets in, they will migrate to the Mediterranean. This generation is the offspring of the butterflies that migrated to the UK in the spring, from southern countries, as far as Morocco. They arrived, mated, laid eggs, and the caterpillars fed on thistles, with the new generation being the fresh painted Ladies that will migrate south. Painted Ladies have mass migration years, in which they are much more numerous than usual, and these years appear to coincide with warm summers when Hummingbird Hawkmoths and Silver Y moths also migrate in large numbers to the UK. The last mass migration year was in 2009.
 If you see Painted Ladies, you can contribute to the research into their migrations reporting your sighting to Butterfly Conservation Migrant Watch Survey.
  See previous posts on Painted Ladies in BugBlog.

The intricate patterns of the underwing of Painted Lady

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Little riders on the wind

The mass influx events of Painted Ladies - such as during the summer of 2009 - and wildlife documentaries on the Monarch Butterfly have made butterfly migration familiar to everybody. Many butterfly species are now known to carry out bidirectional migrations, for those of the northern hemisphere, towards the north in the spring and towards the south in the autumn. Surprisingly, the extent of fascinating behaviour was only recognised relatively recently. Up to the 1930s, the only butterfly that was acknowledged to migrate was the American Monarch, Danaus plexippus, with evidence for migration in other species dismissed even from experienced entomologists and lepideropterists as "overflow": one way dispersal movements from successful, very dense populations. One early researcher was set to change matters: Carrington Bonsor Williams (widely known as C.B.), from Rothamsted Experimental Station in the U.K. He was passionate about insect migration and amassed large amounts of data on the subject, in Britain and abroad. In his 1930 book Migration of Butterflies and later work, he presented evidence for migration for over 200 species of butterflies worldwide, including support for return migration. He also helped organise the collation of data collected by naturalists across the U.K. on insect migration. His analyses of these data gave strong evidence for migration for six species of British butterflies: the Painted Lady, Small Tortoiseshell- which also hibernates in the U.K. - , Red Admiral, Large White, Clouded Yellow and Pale Clouded Yellow. For the Red Admiral, the records  showed clearly a dominant proportion of individuals flying in a northerly direction up to the end of July, and a southerly direction during September and October:

(Figure from Williams 1951)

In the case of the Painted Lady and the Large White, the lack of evidence for a return migration puzzled Williams:

I have already (Williams et al. I942, p. 250) pointed out the difficulty of accounting for the persistence of a habit of movement in one direction only on any theory of evolution. If we accept that directional movement in butterflies is simply an overflow from an over-populated area, and that none of the emigrants ever return; then the species must be perpetuated by the offspring of those individuals which do not emigrate. Thus a habit must persist for countless generations, in spite of the fact that all  individuals which develop it die without contributing to the continuity of the species.

He was optimistic though, and correctly predicted that return flights would be found in all species once enough research effort was put into it, making butterfly migration as important a phenomenon as that in birds. Indeed, recent research - some of it carried out in Rothamsted - including meteorological analysis of prevailing winds when influxes of Painted Ladies occur, and entomological radar research has shown that the Painted Lady taked advantage of tailwinds as a migratory aid and that the reason that these flights were not detected is that they fly at high altitude.
 Migrating butterflies are tracking suitable breeding grounds, areas where larval food plants are abundant. Red Admiral caterpillars feed on fresh, rapidly growing nettles. At the end of spring, nettles start to wither in the Mediterranean winter grounds, so the spring Red Admiral adult generation flies to Northern Europe - and also up mountains - where nettles are luscious. They mate and lay eggs in the north and the resulting autumn generation of adults migrates due south in the autumn.

(Figure from Mikkola 2003)
Unlike birds, butterflies breed both in the winter and summer grounds, and also unlike birds, each generation makes a one way trip, leaving the return journey to their offspring.
(Photo above, a fresh, autumn generation Red Admiral feeding on Cherry Laurel, 19 Aug 2011)

References
Williams, C. (1951). Seasonal Changes in Flight Direction of Migrant Butterflies in the British Isles The Journal of Animal Ecology, 20 (2) DOI: 10.2307/1537

Kauri Mikkola (2003). The red admiral butterfly (Vanessa atalanta) is a true seasonal migrant: an evolutionary puzzle resolved? European Journal of Entomology, 100, 625-626


Stefanescu, C., Alarcon, M., & Àvila, A. (2007). Migration of the painted lady butterfly, Vanessa cardui, to north-eastern Spain is aided by African wind currents Journal of Animal Ecology, 76 (5), 888-898 DOI: 10.1111/j.1365-2656.2007.01262.x

Chapman, J., Nesbit, R., Burgin, L., Reynolds, D., Smith, A., Middleton, D., & Hill, J. (2010). Flight Orientation Behaviors Promote Optimal Migration Trajectories in High-Flying Insects Science, 327 (5966), 682-685 DOI: 10.1126/science.1182990

Warming up painted lady

Cloudy, with intermittent showers today. A cold Painted Lady sat 'shivering' on a bush in the garden and allowed me a close approach. The shivering appearance was due to the butterfly revving its flight muscles, what I had never seen before. I have to apologize - to the butterfly - that I had to use flash, as it was dark and I wanted to emphasize the effect of its wings movement. A few moments later, the butterfly flew away.

A view of the Painted Lady's wing underside.

On this frontal shot the first modified pair of legs are visible just under the butterfly's eyes. 

Home-grown Painted Ladies

All of a sudden, Buddleia blooms across the city today were decorated with fresh-looking bright coloured Painted Ladies (Vanessa cardui). The contrast with the faded, worn first individual I photographed this year (see this previous post and also an extreme example here) was stark. Most of today's butterflies were likely to have been born in the U.K., the offspring of the migrating individuals. It is unclear how many generations of Painted Lady happen every year, as there is a lot of overlapping. According research carried out by the Spanish researcher Constanti Stefanescu, the whole cycle outdoors takes 6 to 8 weeks depending of the temperature, and he estimated 3 to 4 generations for NW Spain. The number of generations must be more limited here, with the cooler climate, and is likely that these fresh-looking butterflies will become the returning generation and they are not interested in breeding anymore, but in fattening up for their lengthly return to North Africa

Feeding against the sky

A fresh Painted Lady sunbathing on a wall

More information
Stefanescu, C. (1997) Migration patterns and feeding resources of the Painted Lady butterfly, Cynthia cardui (L.) (Lepidoptera, Nymphalidae) in the northeast of the Iberian peninsula. Miscel.lania Zoologica, 20: 31-48.

Painted Lady mass migrations

I have just reported the first Painted Lady (Vanessa cardui) of the year to the Butterfly Conservation Painted Lady Survey. It settled today on my large buddleia, now covered in full bloom, and fed for a log time, fluttering from one bloom to the next (photo above). It has been a long wait considering the species has been on the news for a few months now. Painted ladies are strong flyers and migrate every year into nortern latitudes in search of foodplants and nectar, but migrations vary in their strength several orders of magnitude (see graph).

(From Stefanescu et al 2007)

Mass migration of butterflies occur every 6-10 years, as the last large migrations on this years scale in 1996 and 2003. The last couple of years have been quite poor. This year, in contrast, from a handful of sightings before May, thousands of migrating Painted Ladies were reported in the UK starting from southern England. This butterfly species overwinters in the semidesertic areas of North Africa but also of Mexico and Asia, as it is a cosmopolitan species. Depending of climate fluctuations such as El Nino, higher rainfall than usual in these regions make their larval foodplants - many, but mainly mallow and thistles - flourish, together with the butterflies. The newly emerged adults then start a northwards migration following their foodplants and nectar. Most records of migrating Painted Ladies are of individuals migrating in a given direction near the ground. However radar data of other migrant butterflies - the Monarch and the Red Admiral - documenting them migrating from 1000-3000 m high, sometimes rising with thermals and then gliding down with the aid of tail-winds towards their destinations, an energy-efficient and faster migration strategy than flying close to the ground. A recent study by Stefanescu and collaborators used an indirect approach to study how Painted Ladies migrate. They tested the idea that Painted Ladies migration from North Africa to southern Europe happens high up in the atmosphere aided by tailwinds. They tested whether butterfly peak records were associated to winds blowing from Africa - winds laden with Saharan dust are common in Spain in Spring. The data showed a clear effect of Northerly winds from North Africa in the sudden appearance of visibly migrating Painted Ladies in many localities of NE Spain. These results indicate that the butterflies use the wind to migrate more economically and doing so often flies high up over the ground. The flights close to the ground might reflect periods during the migration in which wind conditions are not favourable high up. The butterflies fly both by day and night and often over vast distances over the sea (there are records from fishing boats and oil rigs tens to hundreds of miles off the coast. Mysteriously, and contrasting with the spectacular spring migration, there is little evidence of the autumn return migration of the Painted lady -although the suden appearance of high numbers of butterflies in their winter grounds suggests that it does happen, as one could predict based on evolutionary grounds. There is hope that future analysis using radar might reveal if these butterflies return to Africa mostly flying high up, where their movements are difficult to observe and where they take advantage of fast winds. This is what Rebecca Nesbit, who is carrying research into the Painted Lady migration thinks could be the explanation.