This spectacle is probably due to both the emergence of locally-bred butterflies and the immigration of Red Admirals from other parts of Europe.
Strong, capable fliers, Red Admirals regularly undertake migratory journeys of hundreds of miles, typically in a northerly direction in spring/early summer and then southwards in the autumn.
In this way, they track favourable climatic (and, therefore, vegetation) conditions that enable the Red Admiral to breed continuously throughout the year.
Most other butterflies have to take a winter break (hibernation) in cold northern countries or a summer break (aestivation) in hot, dry southern ones.
In Britain and Ireland, early autumn often sees the final arrivals of Red Admirals from the south, at the same time as others pass through from the north heading southwards.
As an added complexity, in the past decade or so, Red Admirals have started to remain in Britain and Ireland throughout the winter.
They do not enter hibernation but remain active on sunny days and, hence, this species has suddenly become our most commonly sighted winter butterfly. Breeding continues too, with territorial and courtship behaviour observed and developing caterpillars found throughout the winter.
It is not unexpected to have plenty of Red Admirals in our gardens and countryside at this time of year. Indeed, large numbers were reported widely during late summer and autumn last year too.
What was very noticeable this year, though, was the lack of Red Admirals (and many other butterflies) from our gardens during the main part of the summer. This is not usual. Red Admirals are normally widespread and numerous, particularly in the south, during July and August as, indeed, they were in 2011.
The decrease in Red Admiral numbers in summer 2012 is reflected in the results of Big Butterfly Count, which showed a big year-on-year decrease for this species, among many others.
It is unlikely that the recent surge of sightings, welcome though it is, will make up for the paucity of Red Admirals over the course of the summer.