Migrant Red Admirals Vanessa atalanta (L.), usually arrive in the UK during May and June each year. Like the closely related butterfly, The Painted Lady, Vanessa cardui (L.), these migrations of Red admirals originate from countries around the Mediterranean – possibly as far south as the North African coast. (2) The butterflies fly north on southerly winds to feed on new growth as it becomes available in the Spring (1).

Most European Red Admirals  migrate north in the Spring and – after producing a new generation – migrate south again in the Autumn. (3)  This seasonal movement appears to occur right across Europe and western Asia, although this still needs confirmation from many regions, with waves of migrants moving north, for example up into Finland, northern Norway and northern Russia. (4, 5, 9, 10).

Red Admirals arriving in the UK, mate and lay their eggs mainly on stinging nettles (Urtica diocia); a new generation emerges sometime over the period, August to October.  A small number of Red Admirals remain to overwinter in the British Isles (mainly in southern England) – although numbers appear to be increasing with climate change – whilst the majority elect to migrate. (3) How does this choice to migrate or not work in practice? “Should I stay or should I go now”?! (6). Perhaps a small proportion of the population are genetically programmed not to migrate?

Of those individuals that remain in the UK, it is not thought that they hibernate in a physiological sense, although many sites state that they do hibernate, I think it is true to say that they merely remain dormant, since they can become active on sunny days throughout the winter. (5)  Some of these remaining butterflies must mate in the autumn, as there are records of V. atalanta larvae developing slowly over winter. In other words, a second generation gradually develops over the period from autumn until the following spring. This is exactly what happens when the migrants arrive back in Spain in October and early November as well; ‘larval development occurs throughout the winter until a first annual generation of adults appears in early spring’ (Stefanescu, 2001). (3)

The small proportion of the UK population which do not migrate south are in effect opportunists, which presumably do well in mild winters but suffer heavy mortality in cold ones. The home-grown adults appear in early spring in the UK, well before the next wave of migrants arrive from southern climes, but the overall contribution of these overwintering individuals is thought to be minimal; populations in northern Europe were considered to be entirely dependent on immigration which determines abundance (8). This situation may however, be changing as the climate warms.

Red Admirals flying southwards in September, in Finland, were found to migrate on sunny days when cool northern winds were blowing (13). Red Admirals take about 5 weeks to fly the 3,000 km from Northern Europe down to the countries surrounding the Mediterranean (1). Circumstantial evidence from meteorological radar observations suggests that they migrate at high altitudes (up to 2,000m or more), where temperatures may be as low as 2-3 deg C! Once they arrive in the south again, in places such as the Catalonia lowlands in north-east Spain – in October and early November, they start breeding a new generation. (2)

Not all Red Admirals migrate over long distances. Studies in Spain by Stefanescu (2001) have shown that some individuals fly much shorter distances towards nearby locations of a high altitude. The butterflies shown here (e.g. above and below) feeding on bell heather were photographed in late August at one such location, near the peak of a hill in Galicia, Spain.

Citizen science projects, such as the one on Red Admiral migration run by the Insect Migration & Ecology Research Group, at the University of Bern, Switzerland (13), offer enormous potential for gathering information on insect migration. People all over Europe can record sightings on a plethora of citizen science portals – some of which are configured as easy to use Apps – allowing researchers to build up unprecedented data bases of records in time and space. It will be fascinating to see what they can come up with in terms of new findings.

1. Stefanescu, C., Alarcón, 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.
2. Brattström, O., Bensch, S., Wassenaar, L. I., Hobson, K. A., & Åkesson, S. (2010). Understanding the migration ecology of European red admirals Vanessa atalanta using stable hydrogen isotopes. Ecography, 33(4), 720-729.
3. Stefanescu, C. (2001). The nature of migration in the red admiral butterfly Vanessa atalanta: evidence from the population ecology in its southern range. Ecological Entomology, 26(5), 525-536.
4. Fox, R. & Dennis, R. L. (2010). Winter survival of Vanessa atalanta (Linnaeus, 1758)(Lepidoptera: Nymphalidae): a new resident butterfly for Britain and Ireland?. Entomologist”s Gazette, 61(2), 94.
5. Bolotov, I. N., Bochneva, I. A., Podbolotskaya, M. V., Gofarov, M. Y., & Spitsyn, V. M. (2015). Butterflies (Lepidoptera: Papilionoidea and Hesperioidea) from meadows of Vinogradovsky District, Arkhangelsk Region, northern European Russia, with notes on recent intense expansion of the southern species to the north. Check List, 11(5), 1727.
6. https://www.youtube.com/watch?v=BN1WwnEDWAM (The Clash video).
7. http://nurturing-nature.co.uk/wildlife-garden-videos/red-admiral-butterflies-do-they-hibernate-in-britain/
8. Pollard, E., & Greatorex-Davies, J. N. (1998). Increased abundance of the red admiral butterfly Vanessa atalanta in Britain: the roles of immigration, overwintering and breeding within the country. Ecology Letters, 1(2), 77-81.
9. Brattström, O. (2007). Ecology of red admiral migration. Department of Animal Ecology, Lund University.
10. Brattström, O., Åkesson, S., & Bensch, S. (2010). AFLP reveals cryptic population structure in migratory European red admirals (Vanessa atalanta). Ecological Entomology, 35(2), 248-252.
11. Peter B. Hardy. The Butterflies of Greater Manchester. http://www.oocities.org/pgll@btopenworld.com/bgm/bgm.htm
12. Mikkola, K. (2003). Red admirals Vanessa atalanta (Lepidoptera: Nymphalidae) select northern winds on southward migration. Entomol. Fenn., 14(1), 15-24.
13. https://insectmigration.wordpress.com/red-admiral-migration/