Clouds of butterflies have been sighted in southern Britain this summer but wildlife lovers are being urged to help scientifically assess whether our insects are really bouncing back by joining the world’s largest butterfly survey.
The Big Butterfly Count begins on Friday with reports of an unusually good year for butterflies but ecologists warn this could be a mistaken perception, and 2017 is simply a modest improvement on last summer – the fourth worst year for butterflies since scientific monitoring began.
“We find that what looks like a good year nowadays is only an average year back in the 1980s,” warned Richard Fox of Butterfly Conservation, which runs the annual survey.
The total abundance of common butterfly species has fallen by a quarter since monitoring began in 1976, with drastic declines for once-familiar butterflies such as small tortoiseshells, peacocks and gatekeepers. Recent research has also revealed pronounced declines in urban butterflies over the past 20 years.
The once abundant gatekeeper has declined by 44% since 1976, despite its habitat not being threatened. Photograph: Mark Searle/Butterfly Conservation
Sir David Attenborough, the president of Butterfly Conservation, said: “Worryingly, we are now seeing the fortunes of some of our once common butterflies mirror those of our rarest species and they too are now also suffering significant declines, with butterflies declining more rapidly in urban areas than in the countryside.
“In the last decade our butterflies have experienced several poor years and although resilient, they simply cannot sustain repeated losses, especially if the habitats they need in order to rebuild their populations are also under threat.”
The signs are good this year with butterfly spotters reporting “clouds of butterflies” on nature reserves and meadows in southern England, according to Fox. Marbled whites and ringlets are particularly numerous and some regular butterfly recorders have counted 1,000 butterflies on their weekly counts.
There may not be large numbers of butterflies in gardens – or in northern Britain – yet but Fox said that these should emerge later this summer, with large numbers of small tortoiseshell and peacock caterpillars spotted on nettles this month. These species usually emerge to feed on garden flowers before their winter hibernation.
For participants in the Big Butterfly Count – where people take 15 minutes to count butterflies in their local park, woodland or garden – the sightings offer hope that they will count more than in 2016, which was the worst year in the seven-year count’s history.
Scientists hope the data gathered will help solve riddles such as the mysterious decline of the once-common gatekeeper. Despite its caterpillars feeding on common grasses, this abundant hedgerow butterfly has declined by 44% since 1976.
According to Fox, its decline shows that butterflies and other insects are not just vanishing because of habitat loss but that climate change – and chemicals such as neonicotinoids – must be having an impact.
“Our focus is shifting as conservationists,” said Fox. “It’s not just the specialist [rare] butterfly species we need to worry about. There’s a much more pervasive problem that we don’t really understand. The things that gatekeepers and small tortoiseshells eat – nettles and grasses – are still there. So there’s something else going on.”