2022 heatwave and drought impacted butterfly populations, results of latest UK Butterfly Monitoring Scheme show
The heatwave and subsequent drought last summer has had a 'major negative impact' on UK butterfly species, a study has confirmed.
Extreme weather, experienced by many areas of the country last year, has drastically affected butterfly numbers according to results from the latest annual UK Butterfly Monitoring Scheme, which suggests the weather could have pushed some species closer to extinction.
Familiar garden and countryside butterflies such as the green-veined white, small white, small tortoiseshell, peacock and brimstone had appeared in good or average numbers during the spring and early summer, suggest official figures.
But after widespread drought conditions last July and August, numbers in the subsequent generations were greatly reduced and scientists fear further damage to populations will be noticed when they start to emerge again this year.
Drought impacts the offspring of butterflies which are flying during the hot dry weather because it causes the plants that caterpillars rely on for food to wither and die.
Without sufficient food, many caterpillars fail to survive, leading to lower numbers of butterflies in the next generation.
For some UK species that have more than one generation in a year, the resulting major decline in numbers has already been seen, says the study.
However, for others, the next generation won't emerge until this summer, meaning there could also be noticeably fewer butterflies around in 2023.
It’s not the first time butterflies have been affected by a drought in the UK. Data gathered by the UKBMS shows that in both the record summer of 1976 and again in 1995, that heat hit butterflies hard.
Some species, say those involved in the study, never recovered from the 1976 drought - albeit habitat destruction is also likely to be a major factor in their failure to bounce back.
But the difference between last year's drought, compared to that of 1976, is that by 2022 many UK butterfly species were already in decline - with Butterfly Conservation’s State of the UK’s Butterflies 2022 report suggesting that 80% of butterflies have declined in abundance, distribution or both since the 1970s.
And with numbers finding it increasingly hard to recover there are fears more frequent and severe droughts, brought on by climate change in the coming years, will only do more damage to populations and push some species further towards extinction.
Butterfly Conservation’s Head of Science, Dr Richard Fox, said: "Overall, the data for 2022 tells us that it was an average year for butterflies. However, it was a year of two halves with butterflies seen early and in about average total numbers (compared to the last 10 years) from April to July but then in greatly reduced abundance after the summer heatwave and drought.
"In general, warm, sunny weather is good for butterflies as they can be active, finding food, mating and laying eggs. But drought is a major problem as plants wither and die, meaning female butterflies may struggle to find anywhere to lay their eggs, or there is not enough food for the caterpillars when they hatch.
"The knock-on effect is fewer butterflies in the following generation. We have already seen an indication of this in the 2022 data for some of those species with a generation that flies in late summer and autumn, and sadly we can expect to see a decline in numbers of other species in 2023 too."
While 2022 was a terrible year for some species there is hope others like the purple emperor, large blue, chequered skipper and dark green fritillary - all of which have been the focus of targeted conservation work over the last few years - may have fared better should numbers emerging this summer also hold up.
The chequered skipper butterfly was reintroduced to Fineshade Wood in 2019 with conservation work proving so successful that the location was revealed last year.
While the UKBMS data can help target those species most in need of conservation work, butterfly populations do fluctuate naturally from year to year, largely due to the weather, while the long-term trends of are mainly driven by human activity, particularly the deterioration of habitats, and climate change.
Dr James Heywood, from the British Trust for Ornithology, whose volunteers collect butterfly data through the wider Countryside Butterfly Survey, said the information can also help track the health of other animals.
He explained: "These data are incredibly valuable as butterflies are indicators of the health of our natural environment and therefore the information gleaned from the UKBMS data is not just used to help understand and conserve butterflies, but also to help understand and protect the wider ecosystem on which so many birds, mammals and other species rely."