Hi everyone,
Last year on August 29th I came across a few pristine Silver-studded Blues on a patch of heathland in Dorset, which I assumed were 2nd brood individuals. I've been trying to find out some more information on 2nd brood SS Blues in the UK but so far I've found very little, does anyone have any more info on how regular an occurrence this is? Also, the summer of 2008 seemed pretty terrible weatherwise, what conditions might've caused a 2nd brood to appear? I looked in the same spot this year in late August just to see if any were around but unfortunately I drew a blank!
Here's a shot of one of the individuals:
whilst visiting matley bog in the new forest on august 31st this year, with paul brock we found a late female ssb, id guess that they were just late individuals also and not a second brood as they over winter as eggs. only a guess and im sure someone else on the site will have more knowledge of their life history and maybe confirm one way or the other.
As far as I am aware (ie. I could well be wrong) the only locality to have produced a confirmed second brood of Silver Studded Blue is a site on the Atlantic coast of Cornwall. A phenomenon that has been observed since the late 90's.
Detailed observations over the past decade have confirmed that this species is capable of producing a definite defined partial second generation with a distinct gap between both broods, thus following the habits of this species in southern Europe where a second generation is the norm in some regions. The flight period of this second generation in Cornwall generally begins over the last week in August and seldom lasts beyond the second week in September.
As for your specimen, things are not so clear cut. Very late specimens have been recorded in Dorset and the New Forest (such as Gary's example) however there is little evidence that this is actually a second generation. The flight season of the Cornish coastal colonies is much earlier to start with, providing a distinct gap between broods. Significantly, the Cornish second generation is typified by a (small) flush of pristine adults, rather than just one or two lone sightings.
The short answer is that your specimens (and Gary's) could be the offspring of a female that flew earlier this year as a second generation is clearly possible in favourable microclimes, especially as you say that you saw more than one pristine example. However, it is equally as feasible that these specimens are very late emergences caused by the retardation of larval and pupal development for some unidentified reason.
Having said all that, it's certainly an interesting sighting, and it's certainly well worth a look again at your sight in a favourable year.
Birds foot trefoil (Lotus corniculatus), the foodplant used almost exclusively on the dune-system colonies in Cornwall. Of course it's not known yet whether this partial second brood produce a viable progeny themselves, or whether it is a dead-end. As far as I am aware (and again I am keen to be corrected if this is not so) no one has observed successful egg laying in this generation.
Interesting. I asked because I wondered whether it was even possible for colonies based on heather to produce a second generation, given that the heather doesn't produce succulent shoots until the spring (I must admit, I don't know which bit of the heather the caterpillars feed on, because I've never found any). On the continent there is a huge variety of foodplants and I imagine something like bird's foot trefoil, which is fresh almost all year round, is much more suitable for squeeezing in a quick summer brood.
Thanks very much for all the replies, especially Felix, that is very interesting stuff! I will try and make regular visits over the course of the next summer and see what I can find, although I suppose it must be incredibly difficult to determine whether a late butterfly is from a second brood or not!
Thanks again for your help,
Guy
It might be worth looking at the Great Orme colonies in North Wales as they emerge a couple of weeks earlier than normal and use B F Trefoil. I have certainly seen ss Blues there as late as mid August some years.
My experience of the North Shropshire colony over almost 30 years is that, that colony ofter starts emerging soon after mid-June and continued into early August, although in the case of that colony Heather appears to be the foodplant.
