Dear Readers, although it’s been a cool and wet couple of weeks, I have been enjoying watching the butterflies on the buddleia outside my office window. My perception was that there has been a huge uptick in the insects this year – as I’ve mentioned, at one point there were no less than six Red Admirals on the plant at the same time. Even as I look out of the window on this wet and windy afternoon, there is a Red Admiral perched on the flowers, hanging on as the whole bush shifts through about 120 degrees backwards and forwards. But individual anecdotal information, though it tells an interesting story, is not as solid as data collected by a whole range of people, and the information coming through from Butterfly Conservation Trust’s Big Butterfly Count (which ends on Sunday 6th August) is utterly compelling. So far, over 170,000 sightings of Red Admirals have been recorded, a 400 percent increase on last year. So, what is going on?

Some  Red Admirals have always overwintered in the UK  – you will get occasional reports of people finding the insects in their sheds or lofts, and you can see Red Admirals feeding on mild days throughout the winter. However, the historically the vast majority of the butterflies have been migrants – Red Admirals used to spend the winter in the milder parts of southern Europe every year and then, when their foodplants dry up in the spring(their eggs are laid on the stinging nettles upon which the caterpillars feed) they start to move north, reproducing as they go. Peak numbers arrive between July and September.

In August/September, the adults start to head southwards back towards mainland Europe, feeding on ivy, windfall apples and damaged soft fruit and sap. I am tempted to try my ‘rotten banana’ experiment again this year – just as in tropical butterfly houses, UK butterflies (especially those fattening up for a migration) are sometimes glad of some easily digestible sugar. By the time they start their journey home, female Red Admirals in particular are full of fats, for good reason – they are already carrying next year’s unfertilised eggs, and when they reach southern Europe again they will look for a mate, so that the whole cycle can begin again.

Why, though, are there such huge numbers this year? One explanation is that, with the milder winters due to climate change, more Red Admirals are staying put, especially in the warmer south of the UK, and the chances are that more of them are surviving. Red Admirals seen early in the year are likely to be ‘homegrown’, either because they’ve over wintered as adults or hatched from eggs laid much earlier in the year. Numbers are then swollen by migrants from Europe, and my (untested) hypothesis is that, with the very high temperatures and fires right across southern Europe and North Africa, the butterflies are being driven north because their larval foodplants are either dry or burnt. I have a suspicion that more insect species, previously confined to mainland Europe, will arrive on our shores over the next few years/decades, and creatures previously confined to the south of England will be able to make their homes further and further north. What will happen to cold-climate and high altitude specialists remains to be seen, as they run out of places to live as the temperature rises. All I do know is that the situation will be complicated and difficult to predict.

I will be fascinated to see the final results of the Big Butterfly Count. I am sure there will be more surprises. Personally, I have seen far fewer Comma butterflies this year, and very few Small Tortoiseshells, though I am pleased to have seen plenty of Peacocks and a few Painted Ladies. Let me know if you’ve noticed anything unusual, or if you’re also seeing a lot of Red Admirals. It’s interesting to see what’s going on around the country, for sure.

Peacock butterfly