Queensdown Warren late in the day

Lots of Meadow Browns and Two Marbled White Butterflies between 4:30 and 7:30 this evening.

This is a Marbled White, Melanargia galathea. This is a female, recognisable by the yellowish tinge on the underside of the wings, the males are more monochrome black and white. There are only four functional legs in both males and females in the family of Brush-footed Butterflies, Nymphalidae, the Browns, subfamily Satyrinae, the front pair of legs being converted into a small pair of "brushes". Incidentally, the stem behind is an Agrimony, Agrimonia eupatorium, stem going to fruit, remarkably beautiful.

This is the peak month for this butterfly and they should be dropping their eggs over the potential grass larval food plants from around this weekend onwards. This is a typical pose for these butterflies in the afternoon, either on grasses or their nectar source flowers. In the morning they tend to rest with their wings spread to warm up, and for the rest of the day of course they are generally much more active. Unimproved tall grassland is their typical habitat, particularly chalk downland, but even small patches of verge with tall grass will sometimes support small colonies. The Marbled White is a strong flier and a good disperser, so should be fairly good at surviving in the patches of grassland still available on the North Downs, according to research in Belgium and Germany. However the more patches there are, the easier that survival should be.

The Butterfly appears to be spreading slowly North and has most likely recolonised most of Europe from different glacial refuges around the Mediterranean. North Africa and specifically the Maghreb may also have been involved. There are two sibling species, Melanargia galathea that is thought by some to have expanded back into Europe after the last glaciation from two separate refuges in Italy (Western population) and the Balkans (Eastern population) and Melanargia lachesis that is currently found only in Spain and Southern France. The species split itself may have occurred much earlier in the glacial/interglacial cycles, but the mutual interactions of the two species raise several interesting questions about competition, dispersal and evolution. It is interesting to note that the form known as ssp serena is distinguished as the form found in Britain, which derives from the Western population of Melanargia galathea and which must also be a founder effect at the time of the cutting of the land bridge.

The subspecies include serena in Britain, galathea in Europe and the South Urals, donsa in the Caucasus, satnia in the Caucasus major and minor, lucasi in North Arfrica, and tenebrosa.  However I know little about the rest of the species' populations spread across Asia as far east as Japan.

The high genetic diversity and the relatively strong differentiation of the four African populations sampled in a
comparatively limited area of the Atlas Mountains indicate that the most probable origin of the species Melanargia galathea is northern Africa, with its sibling species, M. lachesis, evolving in parallel in Iberia. Most probably, M. galathea colonised Europe first during the Eem (last before this one) interglacial, some 130 ky ago. Since M. lachesis must have existed on the Iberian peninsula during that period already, M. galathea should have reached Europe via Italy. The genetic differentiation to distinct groups in Europe most probably evolved during the following (most recent) Wu¨rm glacial period.

There is a lot of genetic diversity in Melanargia galathea, but this is well mixed within its habitat patches and amongst the wider populations, due to the species' movement ability. The genetic diversity may have arisen partly as founder effects of the small populations isolated in refugia at the time of previous, and in particular the last, glaciation. The species may now in theory require this continuing diversity and intermixing and may be vulnerable to further habitat isolation if the genetic diversity is consequently severely reduced.

The distribution on the chalk in Kent is primarily Eastern according to Thomas and Lewington, and admittedly these are the most Westerly ones that I have seen so far in this county. On the other hand I have seen them in good numbers at Oxford services, so its not all about latitude! Other observers in Kent have also seen numbers to the West, at Darland Banks, Borstal, Lullingstone and Cobham, so the distribution in Kent may have evened out a bit.

This on the other hand is a male, not so well focussed sadly, seen a few moments later on a Large Knapweed, Centaurea macrocephala, flower.

Red Fescue, Festuca rubra, is thought perhaps to be an essential larval food plant, and it picks up some toxins from a fungal infection of that plant, which are apparently carried through into the adult body. However the larvae do feed on a range of other grasses.