Best Of 2012 - August
By far the biggest 'winner' of 2012, of which there were really only two in Sussex, was the Chalkhill Blue. Unprecedented numbers emerged on some sites, with the combined estimate for the peak days at Friston Gallops and Amberley being in excess of 1 million butterflies, at densities of up to 33 per metre square and considerably higher when concentrated at roost. It seems that the soaking summer had allowed atypically profuse growth of lush, nitrogen-rich Horseshoe Vetch plants, capable of supporting a vast number of caterpillars; food-plant availability may well be a major factor in limiting population size in most years. With so many Chalkhill Blues around it was very easy to find aberrant forms and I discovered good numbers of ab.
postcaeca at Friston (male and female examples below - first and last images). Adventurous males were seen 17.5 miles north of this site, well away from the Downs.
The Adonis Blue, the larva of which has subtly different requirements in terms of Horseshoe Vetch growth form, did not fare so well. A poor first brood was followed by a very patchy second, with only the very best-drained and warmest sites producing good numbers in August. Elsewhere the summer brood was very weak.
Small Heath did well in the spring but had a poor second brood, while Speckled Wood and Essex Skipper fell just on the wrong side of average. The Peacock had a relatively poor season and the summer brood emerged two weeks later than in recent years, subsequently going into hibernation very quickly.
Both of our late species, the Silver-spotted Skipper and Brown Hairstreak, had quite average seasons, but better weather through their flight periods will have allowed good egg-lays and bodes well for 2013. Warm, anticyclonic conditions may also have assisted colonisation of new sites, so it will be high on my list of priorities next year to look at currently unoccupied habitat patches close to existing populations.