As the summer of 2025 slowly slips away, the consensus among butterfly enthusiasts is that it was good year for these colourful insects. May was the sunniest May on record, June was warmer than usual and Met Éireann reported above average temperatures in July.
The summer of 2023 was unusually wet, and the summer of 2024 was unusually cold resulting in a butterfly populations crash. However, improved weather conditions during the summer of 2025 saw a recovery and a rebound in butterfly numbers.
Weather impacts significantly on the development of butterfly eggs, the growth of caterpillar foodplants, the behaviour pf predators, etc.
A fine May and a fine September prolong the summer and are a welcome bonus to species like the very common Small Tortoiseshell that can produce more than one generation during the breeding season. Some can even push it to fitting in a third generation if the early autumn stays settled and fine.
Some of our butterflies are migrants like the well-known Red Admiral. The heat dome that was pretty stationary during the recent summer over southern Europe and the Mediterranean basin promoted healthy butterfly populations there and accelerated the movement north of migrants. When more migrants arrive here and when the weather stays fine these visitors from mainland Europe can successfully breed in Ireland.
When I was on the nature trail recently I paid particular attention to what butterflies were about. I was on the coast, and species were scarce. A lone Red Admiral was resplendent showing that it had very recently emerged. A white butterfly flitted briefly in the distance, too far away to be sure what it was. Common Blues were the most abundant species followed by Painted Ladies.
Then to my surprise a Clouded Yellow drifted lazily by unmistakable as it is the only golden-yellow species in our butterfly fauna. The Clouded Yellow's home range permanent population is in North Africa and southern Europe. Every year it migrates northwards. In some years few if any arrive in Ireland; in other years good numbers turn up.
The one I spotted was very fresh and considering the lateness in the season it may well have been the offspring of immigrant parents that bred successfully on the chalk grasslands in the south of England. Depending on the weather, more could come up to as late as October, so it is a species worth watching out for.