One of the best known migratory butterflies, the painted lady, undertakes a yearly migration, along what is best described as a ‘continuously breeding migration path’ (Stefanescu. 2013). This annual, multi‐generational round‐trip is essentially a living wave of butterflies which flows north and south each year, with the seasons; in keeping with changes in food resources that follow a predictable climate‐related pattern. Whatever we choose to call it, it is an impressive round-trip of up to 15,000 km! Although, no individual butterfly flies all the way back and forth, the populations move all the way from Africa to Europe and back each year.

In researching this blog, I realised that I have ‘crossed paths’ with migrating painted ladies at a number of locations, at different times in the past, from Morocco, through northern Spain to England. Once I came across a Painted lady nectaring on flowers (below) in a botanical gardens in Barcelona, Spain, in early June. In Catalonia, in north-eastern Spain, the spring migration of V. cardui occurs in April, May and early June. Perhaps it had just arrived from North Africa?

Although painted ladies, Vanessa cardui, have long been known as migrants to our shores here in the UK, and elsewhere, it has taken a vast amount of work by Dr Constanti Stefanescu – based at The Granollers Museum of Natural Sciences, in Granollers, Barcelona, Spain – and his colleagues, including Dr Gerard Talavera – together with thousands of volunteers, citizen scientists – to piece together the whole picture. The Worldwide Painted Lady Migration Project is a citizen science Monitoring Network which studies trans-Saharan migrations all year, and anyone can join and look out for Painted ladies!

Another place I have come across good numbers of Painted Ladies is in Northern Spain. Last year (2018), I found many nectaring on the northernmost headland in Spain – Cape (Cabo) Ortegal (below). Were the butterflies fueling up for a sea crossing? I don’t know.

Painted ladies are fast fliers. They take advantage of favourable winds, and move downwind at heights varying from tens to over 1,000 m above the ground, sometimes flying at average ground speed of ~50 km/h (when higher up). Migrating V. cardui use a sun compass system to select and maintain their flight headings, just like their cousins, the Monarch butterflies do, in North America.

The basic pattern of the migration, appears to be one of  ‘successive displacement and reproduction’ of a vast population that
in some years may be a high as thousands of millions of individuals. They probably pass through about six generations one their way north and south: from the Sahel region of Africa, through North Africa, the Mediterranean, Central and Northern Europe, before moving back to Africa in one or two steps (Stefanescu. 2013).

Europe is effectively recolonised each year from the south. Each spring, painted ladies migrate north from Africa (especially from the Maghreb region), sometimes in huge numbers (as in 1996 and 2009). Massive emergence sites have been found in Morocco, with 155,000 pupae in just 1.8 ha, for example. The maximum abundance was recorded in the Souss valley, a fertile and rural area in mid-southern Morocco (Stefanescu et al., 2011). The butterfly populations build up on thistles, desert nettles and mallows, often under the shade of palm trees. It is a beautiful area, which I was lucky enough to visit in 2011, on the back of a conference in Agadir (see below).

There are many argan trees (below) in this region, from which the valuable argan oil is extracted; an important source of revenue. Remarkably, there is usually a complete absence of Painted ladies in Morocco at the end of summer (mid-to-late September) – they have all gone north – but a huge number of migrants arrive back there in October and early November! (Stefanescu et al., 2017).

The seasonal pattern in northern Europe is usually a spring peak of immigrants in early June and a second, much larger, peak – as result of the progeny of the first wave of immigrants – in late summer. There is also a huge increase in the levels of parasitism as the summer progresses. Otherwise, I guess, we would all be drowning in Painted ladies! (Stefanescu et al., 2012).

I have also come across rather worn individuals in northern Spain, like to one shown below, in September. Were they on their way back south? I expect the local movements are quite complex. Perhaps they follow the coast?

Painted ladies sometimes accumulate on or near hill-tops, as on this occasion in September of last year (2018) when I saw many – together with large numbers of Red Admirals and Peacocks – amongst the heather on the slope of this beautiful hill (below). An idyll!

The reason why these migrant butterflies travel north, when their offspring have a very small possibilities of returning south again, long puzzled biologists (Mikkola, 2003).  There was little evidence for a return south in the autumn, until very recently, when researchers demonstrated the reverse autumn migration. Mass migrations in NW Africa during October and November of each year have now been seen in a number of years and constitute a ‘well-established pattern’ (Stefanescu et al., 2017).

Excitingly, it seems that Painted ladies go even further than north Africa, even crossing the Sahara! Recent work suggests that migrants probably originating from Europe, cross the Mediterranean, the Sahara and the Sahel! A journey of over 4000 km, which would be the longest migratory flight ever recorded for a butterfly in a single generation (Talavera & Vila, 2016).  Some butterflies also migrate north again across the Sahara, but the movements in this region are described as ‘complex’. Nevertheless, it is an astonishing feat and well worth remember when hopefully, we see a nice influx of these migrants to our shores next summer.

References

Mikkola, K. A. U. R. I. (2003). The Red Admiral butterfly (Vanessa atalanta, Lepidoptera: Nymphalidae) is a true seasonal migrant: an evolutionary puzzle resolved?. European Journal of Entomology, 100(4), 625-626.

Pollard, E., Van Swaay, C. A. M., Stefanescu, C., Lundsten, K. E., Maes, D., & Greatorex-Davies, J. N. (1998). Migration of the painted lady butterfly Cynthia cardui in Europe: evidence from monitoring. Diversity and Distributions, 243-253.

Stefanescu, C., Alarcon, M., & AVila, 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.

Stefanescu, C., Alarcón, M., Izquierdo, R., Páramo, F., & Àvila, A. (2011). Moroccan source areas of the Painted Lady butterfly Vanessa cardui (Nymphalidae: Nymphalinae) migrating into Europe in spring. The Journal of the Lepidopterists’ Society, 65(1), 15-26.

Stefanescu, C., Askew, R. R., Corbera, J., & Shaw, M. R. (2012). Parasitism and migration in southern Palaearctic populations of the painted lady butterfly, Vanessa cardui (Lepidoptera: Nymphalidae). European Journal of Entomology, 109(1).

Stefanescu, C., Páramo, F., Åkesson, S., Alarcón, M., Ávila, A., Brereton, T., Carnicer, J., Cassar, L.F., Fox, R., Heliölä, J. and Hill, J.K., 2013. Multi‐generational long‐distance migration of insects: studying the painted lady butterfly in the Western Palaearctic. Ecography, 36(4), pp.474-486.

Stefanescu, C., Soto, D. X., Talavera, G., Vila, R., & Hobson, K. A. (2016). Long-distance autumn migration across the Sahara by painted lady butterflies: exploiting resource pulses in the tropical savannah. Biology letters, 12(10), 20160561.

Stefanescu, C., Puig-Montserrat, Xavier, Samraoui, B., Izquierdo, R., Ubach, A., & Arrizabalaga, A. (2017). Back to Africa: autumn migration of the painted lady butterfly Vanessa cardui is timed to coincide with an increase in resource availability. Ecological entomology, 42(6), 737-747.

Talavera, G., & Vila, R. (2016). Discovery of mass migration and breeding of the painted lady butterfly Vanessa cardui in the Sub-Sahara: the Europe–Africa migration revisited. Biological Journal of the Linnean Society, 120(2), 274-285.