Why Britain's butterflies are desperate for a dry summer

Britain's butterflies are in desperate need of good weather in 2008 or they may experience a population "catastrophe", conservationists said yesterday.

They were dealt a massive blow by the record wet summer of last year, new figures reveal. Many species were already declining and the heavy rainfall may have caused them to disappear in many parts of Britain.

Plenty of sunshine is now essential for populations of many species to recover. Survey figures for 2007, released yesterday, reveal that as a consequence of the wet weather, British butterflies collectively suffered their worst year for more than a quarter of a century. Butterflies do not fly in the rain, making it impossible for them to reach the plants whose nectar they feed on, and heavy rain also means they are unable to breed.

It is feared that in many places, the great washout that was June, July and August may have capped years of population decline, and the knock-on effect on breeding will exacerbate the downward spiral of butterfly numbers. The charity Butterfly Conservation said yesterday: "If this happens, the United Kingdom could be facing a butterfly catastrophe with some species facing extinction in parts of the country."

Eight species had their lowest-ever recorded numbers in Britain in 2007, and two very rare species, the high brown fritillary and the Duke of Burgundy, both already plunging in populations, also suffered badly.

The eight species at an all-time low last year were the common blue, the silver-studded blue, the grayling, the Lulworth skipper, the small skipper, the small tortoiseshell, the speckled wood and the wall butterfly. The figures come from the UK Butterfly Monitoring Scheme, operated by Butterfly Conservation and the Centre for Ecology and Hydrology, which each year collates data collected by thousands of volunteers.

"We know bad weather has a big effect on butterflies, so a bad season is bad at the time," said Martin Warren, Butterfly Conservation's director. "But the problem here is that many species are already declining, and have been for decades. So if you get a bad year on top of years of decline, that will push a lot of species to extinction in quite a lot more sites.

"I would say it was like lights blinking, and this would just flip the switch for lights out, and a local extinction. Imagine your local piece of grassland, with butterfly numbers going down for years – you get a particularly bad year, and that's the year when they disappear."

There have been two other very bad years for butterflies since the UK Butterfly Monitoring Scheme was set up 33 years ago, both stemming from extremes of weather. The worst was 1981, the last really chilly summer of recent times, when the average peak UK temperature was a mere 14.1C.

The other was 1977, which followed the severe drought of the previous summer, from which some of Britain's rarest species have never fully recovered. The increased frequency of extreme weather is a serious concern for the future.

It is ironic that last year's disastrous summer followed what was probably the best-ever spring for butterflies in Britain, when temperatures were so warm, climaxing in the record warm April, that no fewer than 11 British butterflies recorded their earliest-ever emergence dates.

But that was followed by a soggy and chilly May, and then the three months of summer, which were the wettest, taken together, since modern British rainfall records began back in 1914.

The floods not only did huge damage to property and infrastructure but also to wildlife. It is only now that the full effect on butterflies can be seen. Britain has 58 regularly breeding butterfly species – 55 residents, and three migrants from the Continent: the painted lady, the clouded yellow and the red admiral. Rising temperatures have meant that the red admiral has begun to overwinter here, and so could now be considered a British resident insect as well.

The casualties

Speckled wood Pararge aegeria

Aptly named as it often flies in partly shaded woodland with dappled sunlight, the speckled wood, dark brown with creamy white patches on the wings, is expanding its range eastwards and northwards. Males sometimes spiral into the airto chase each other.

Lulworth skipper Thymelicus action

One of our smallest butterflies, only found in south Dorset along a stretch of coast near the village of Lulworth. The dull orange-brown wings are held with forewings above hind wings.

Silver-studded blue Plebeius argus

A rare butterfly, now confined to small colonies in England and Wales. Males blue, females brown. Found in heathland where the silvery-blue wings of the males provide a marvellous sight flying low over the heather.

Common blue Polyommatus icarus

This is the most widespread blue butterfly in Britain and is found in grassy habitats. Male has blue wings with a black-brown border, but females are brown in England (though in Scotland, females can also be blue).

Small tortoiseshell Aglais urticae

With its bright orange, yellow and black wings, the small tortoiseshell is commonly found in gardens. It is one of the first butterflies to be seen in spring but has declined considerably. Nettle-feeder.

Small skipper Thymelicus sylvestris

Small with a darting flight and widespread in southern England and Wales; its range has expanded north in recent years. An insect of high summer.

Wall butterfly Lasiommata megera

Named after its habit of basking on walls, rocks, and stony places, the wall or wall brown is declining substantially in southern England. The light brown undersides provide good camouflage against a stony or sandy background.

Grayling Hipparchia semele

Widespread on the coast and southern heaths, but declining, particularly inland. Rests with wings closed, when the mottled-brown underwing is visible, but appears larger in flight when it extends pale yellow-orange bands.