British ladybirds face rapid extinction after invasion by an Asian interloper

They have a special place in the hearts of children. They're beloved by gardeners as natural pest controllers. But say goodbye to Britain's ladybirds, many of which are now facing extinction within a few short years.

In what is probably the worst case of havoc caused by an invasive species the UK has ever seen, a whole group of British ladybird species is likely to be wiped in short order out by an aggressive foreign interloper, which will also become a major pest.

Harmonia axyridis, the harlequin ladybird from Asia, was first detected in Britain in September last year and known to be a threat to familiar species of our own such as the two-spot and the seven-spot ladybirds, by outcompeting them for the aphids on which they feed - and also by eating them directly.

But scientists have recently realised it is having an effect more quickly than anticipated. Those shiny bright red beetles with their black spots, which generations of children have delighted in, and which gardeners have so long relied on to deal with the aphids (greenfly) eating their roses, will soon be a thing of the past.

Britain's leading ladybird expert, Michael Majerus from Cambridge University, says the harlequin, which has come into Britain from continental Europe, either in flower or vegetable imports, or by flying in directly, poses a dire threat to half of Britain's 46 species. He thinks most of the country will be overrun by 2008, and native species will start to disappear immediately.

Although other non-native species have caused severe problems with British wildlife - for example, the grey squirrel from North America has driven out the native red squirrel - Britain has not so far seen a foreign invader destroy a whole suite of other species, as the harlequin is now likely to do.

"In ecological terms, this is a disaster," Dr Majerus said. "I don't know of a worse one."

The case illustrates the growing danger of invasive species in an increasingly globalised world, and is prompting calls for the Government to bring in tighter precautions against chance arrivals of unwanted foreign organisms, which could cause catastrophic damage to agriculture, wildlife or even human health. An official review of the problem in 2003 said the situation was so dangerous that a specialised agency should be set up to deal with the risk. Although a Bill going through Parliament at the moment is tightening up some regulations, such an agency is not yet on the horizon.

Conservationists are now calling for three British ladybirds to be added as a matter of urgency to the UK Biodiversity Action Plan's list of priority species. The common two-spot and seven-spot ladybirds, and the much rarer five-spot species, are all in the firing line, and inclusion in the list would mean the Government has to act to save them. In reality, there may not be much that can be done, Dr Majerus said. "I think that the harlequin will be over the whole of mainland Britain by the end of 2008 and that native aphid-feeding ladybirds will suffer very greatly and will be expelled to the ecological margins," he said.

The harlequin lives in harmony with other ladybird species across its home range, from Siberia to Japan. But for reasons not yet understood, once outside its area, its effects are adverse in the extreme. In North America, where it was introduced in 1988 as a bio-control mechanism to keep down aphids on crops, it has decimated native ladybird species and become a pest of vineyards, where it clusters on grapes, and of houses, where large groups aggregate in the winter. It was introduced into Belgium in the early 1990s for similar reasons and has had a similar effect, being noticed as a problem by 2000.

Entomologists feared it was only a matter of time before it arrived in Britain. On 19 September 2004 an unusual ladybird found at Sible Hedingham in Essex was subsequently confirmed as a harlequin by Dr Majerus. The publicity this sighting attracted quickly brought in seven separate reports, and it was clear the harlequin had invaded Britain in several places. Since then, Dr Majerus said, it had moved out by up to 45 miles from these sites, and was now well-established from south-west London to Derby. A single pair could produce 2,000 eggs, and there were probably "millions" now in Britain. "There is a huge colony in the cemetery at Great Yarmouth, which most probably arrived on flowers laid on a grave," said Dr Majerus.

Harlequin ladybirds are about a quarter of an inch long, and come either with an orange body with up to 22 black spots, or with a black body with two to four large orange spots. As well as eating the young of indigenous species, and outcompeting them for food, harlequins damage soft fruits such as strawberries and raspberries by sucking out large quantities of juice. When winter comes, they move inside houses. The clusters expel a dark sticky fluid that destroys soft furnishings, wallpaper and carpets.