Wet summers drive five British butterflies close to extinction

Three years of heavy rain and low temperatures made it hard for insects to fly

Five of Britain's rarest butterflies are on the road to extinction after three sodden summers in a row, the charity Butterfly Conservation reveals today.

Headed by the rapidly vanishing Duke of Burgundy, a small but very attractive insect whose wings are a lattice of marmalade-orange and black, the threatened species continued to plummet in numbers or remained at near rock bottom levels during the course of last summer.

The other species of great concern are the high brown fritillary, the pearl-bordered fritillary, the wood white and the Lulworth skipper. Experts believe that the extremely wet weather throughout the summers of 2007 and 2008, followed by the above-average rainfall of July and August 2009, have accelerated a long-term decline in all their numbers. Continuous or heavy rain makes it hard for butterflies to survive, as the temperature is usually too low for them to fly.

As Britain has one of the most impoverished butterfly faunas in Europe – we have only 58 regularly breeding species, compared to more than 250 in France, for example – the vanishing of the five would represent an enormous loss. In the 20th century alone, five British butterflies became extinct – the mazarine blue (1904), the black-veined white (1920s), the large blue (1976), the large tortoiseshell (1980s) and the large copper (1990s), the last having been reintroduced from the Netherlands in 1927. However, the large blue has been successfully reintroduced in the West Country.

Mounting apprehension about the future of the five currently threatened species follows analysis of the 2009 data from the UK Butterfly Monitoring Scheme (UKBMS), co-ordinated by Butterfly Conservation and the UK Centre for Ecology & Hydrology, which monitors 1,000 sites nationwide. Last year was seen as a vital time for butterflies to recover from the two awful summers which preceded it, but July 2009 was one of the wettest months on record and disastrous in butterfly terms.

Concern is greatest about the Duke of Burgundy, a butterfly with a charming name, the origin of which remains a mystery. (No one has an idea why this wee chequered thing should be called after a French nobleman.) It has reached new low points in each of the past three summers and is now at its lowest level since monitoring began, having dropped by 65 per cent in numbers since 2000.

A common sight in woodland clearings 50 years ago, the Duke of Burgundy now has fewer than 80 colonies throughout the whole of the UK. "We are particularly concerned about it," said Dr Tom Brereton, Butterfly Conservation's head of monitoring. "At the start of the century there were about 200 colonies in the country. This number has now more than halved – and most colonies that remain are small. It is a serious situation."

The high brown fritillary, a big, handsome fast-flying insect, now has fewer than 50 colonies and has dropped 52 per cent in the past 10 years, while the floppy and fragile wood white, which needs flower-rich rides in woodlands to survive, is down by 67 per cent over the same period. Another rare species, the pearl-bordered fritillary, had its second worst year in 2009, following a nadir in 2008, and is down by 36 per cent since the millennium.

A surprise new concern is for the tiny Lulworth skipper, found only on the Dorset coast between Swanage in the east and Burton Bradstock in the west (with a single colony in Devon). It is down to under 100 colonies and its numbers show the biggest drop of any British butterfly in the past decade – they are down 87 per cent.

"These species are all very vulnerable and they have two basic difficulties," Dr Brereton said. "There are problems for them in terms of land management across the countryside but also a lot of them are in small and relatively isolated colonies. In a bad year it's easy for a colony to die out and the chance of it being recolonised is pretty slim."

It is not just the rare butterflies that are having a tough time. According to the new data, some relatively common species including the wall brown, the small skipper and the green hairstreak, also remained at very low numbers in 2009. But the small tortoiseshell, which has suffered a serious decline in recent years, made a slight comeback.

The highlight of 2009 was the massive migration of painted lady butterflies, which originated in North Africa and arrived in vast swarms in early summer. At one point it was estimated there could have been over a billion painted ladies in the UK. However, the UKBMS figures indicate that this migration was not quite on the scale of the last big one, in 1996.

Overall, the statistics show a very modest recovery compared with the dire summer of 2008, the worst for 25 years. In addition to the abundance of the painted lady, some butterflies also did well, including the green-veined white, ringlet and speckled wood, which thrive in lush woodland areas and may have been beneficiaries of the damp but not particularly cold conditions.