After a mixed summer for butterfly fortunes the biggest concentration in our garden came during a few golden days at the end of September and start of October. At least six red admirals spent the sunny periods of those days around a cherry tree festooned with ivy, drawn by the allure of the opening of the tiny green and yellow flowers.
Difficult to photograph high in the tree, the accompanying picture comes from earlier in the summer for, in our ever warming climate, red admirals are now a feature from early spring onwards with significant numbers surviving the milder winters to emerge from hibernation alongside peacocks, small tortoiseshells, commas and brimstones.
Until the recent warming of our winters, few red admirals could hibernate successfully and most arrived as migrants later in the summer. Red admiral numbers, according to those recorded during the three-week period of the Big Butterfly Count, have been 75% higher this year than last with more than 73,000 seen, a total about the same as that recorded in the last three years added together. Probably the majority of these were migrants, with the reason for the influx to be looked for in their main breeding grounds around the Mediterranean where favourable conditions in spring can produce a population explosion.
Many more of these than usual would then migrate looking for suitable breeding places and searching for nectar rich flowers. It could be that the heat waves that struck southern Europe from June onwards, culminating in the extreme event dubbed Lucifer in August, resulted in flowers becoming so dried out that nectar was in short supply triggering many red admirals to head north.
By this time of year, those feeding on the ivy in our garden are faced with the choice of gambling on a mild winter, hibernating here and getting a head start on breeding in the spring or heading south and crossing back to their more traditional breeding grounds in southern Europe and North Africa. Of course, unlike migrating birds where both adults and young head south, those red admirals which decide to leave are not the same individuals which either overwintered or which reached Britain earlier in the year but their offspring.
Although the weather may have worked in favour of red admiral numbers in Britain this year, butterflies in general are under threat from climate change with the last ten years showing a trend to wetter summers which affect their breeding and food sources. They are also threatened by habitat loss caused by intensive farming, increasing urbanisation and pesticide use on both farms and gardens.