Warm summer of 2019 gives flight to butterfly numbers

The record temperatures of summer 2019 helped make it the best season for butterflies in 22 years, with more than half of Britain’s species increasing in number.

Last summer delivered a winning combination of warmth, sunshine and rain which ensured that caterpillars fed up on lush plants before emerging as adult butterflies.

The marbled white enjoyed its best year since scientific monitoring began in 1976, continuing its climate-assisted march northwards, and the dark green fritillary enjoyed its third best year on record, its numbers up 51% on the previous year.

The drought of 2018 led to fears of a crash in butterfly populations, particularly among species whose caterpillars feed on grasses that shrivelled up that summer.

Unexpectedly, however, the annual UK Butterfly Monitoring Scheme revealed that plenty of grass-feeding species thrived in 2019 including the ringlet, enjoying its second-best year on record, the meadow brown, which had its fifth-best year, and the rare Lulworth skipper, numbers of which increased by 138% on the previous year.

The monitoring of 3,014 sites by volunteers supported by Butterfly Conservation, the UK Centre for Ecology & Hydrology, the British Trust for Ornithology and the Joint Nature Conservation Committee, showed that summer 2019 was also a notable year for the painted lady. The migratory butterfly flew in from Africa via continental Europe in greater numbers than in any summer apart from 2009 and 1996.

Prof Tom Brereton of Butterfly Conservation said the encouraging results “provide evidence that the overall rate of decline of butterflies is slowing and for some species being reversed”.

He said conservation through agri-environment schemes, increased woodland cover, climate warming and “increases in grazing levels by wild animals and a slowing in the rate of agricultural intensification” had all played their part.

Dr Marc Botham of the UK Centre for Ecology & Hydrology said two warm summers in succession, which allowed population numbers to build up over a longer period, had also contributed to the boom year.

“In addition to record numbers of spring species such as orange-tip and brimstone, it was also encouraging to see annual increases in garden favourites such as peacock and small tortoiseshell, both of which have had some poor years recently,” he said.

Some species, however, are struggling to adapt to rapid climatic changes. The rare heath fritillary saw its annual abundance drop by 34%. Its numbers have fallen by 91% over the long term as a result of climate change and a loss of traditional coppicing in woodlands and grazing on moorland.

The figures show that targeted conservation work is helping many rarer species, including the chequered skipper, up by 175% on 2018, and the Duke of Burgundy, which a decade ago was threatened with extinction but recorded its eighth best year since 1976. Other species benefiting from habitat management include the marsh fritillary, silver-studded blue and silver-spotted skipper, none of which are now in long-term population decline.

“We’re really heartened to see a shift in the fortunes of many of our most loved species,” Brereton said. “The long-term situation for butterflies in general does remain a cause of concern though, with more species declining than increasing since the 1970s.”

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