FOREIGN ladybirds are pushing out their British counterparts, a survey led by an Oxfordshire scientist has discovered.

The harlequin ladybird came to these shores in 2004 and its colonisation – spreading 60 miles each year – has led to a rapid decline in once-plentiful British variants.

The study was led by Dr Helen Roy from the Centre for Ecology & Hydrology, Wallingford, with the help of thousands of volunteer insect spotters.

In one example, the two-spot ladybird declined by 44 per cent in Britain during the five years since the arrival of the harlequin and is now “near the threshold of detection in habitats in which it was previously common”.

The analysis, published this week in the scientific journal Diversity and Distributions, states the harlequin’s growing dominance is probably down to predation and competition.

The harlequin, which was originally bred as a commercial pest controller, was first found in Belgium in 2001 and in Britain and Switzerland in 2004.

Dr Roy, from Crowmarsh, said: “This study provides strong evidence of a link between the arrival of the harlequin ladybird and declines in other species of ladybird, a result that would not have been possible without the participation of so many members of the public gathering ladybird records across Britain, Belgium and Switzerland.”

She added: “Essentially we got data from people’s ladybird sightings.

“It was a wonderful thing to have 30,000 contributors, which gave us fantastic data we could compare to previous studies over the last 20 years.”

The study found seven of eight native species are in decline, with only the large seven-spot ladybird putting up any resistance to the harlequin.

Dr Roy said there is “very little that can be done” about the invader’s foothold in Britain, but said the study gives a broader insight into the introduction of alien species in this country.

Belgian co-author Tim Adriaens said: “At the continental scale, the arrival of the harlequin could impact on the resilience of ecosystems and severely diminish the vital services that ladybirds deliver.”

Fellow report writer Dr Marc Kenis, who is leading studies on the harlequin in Switzerland, said: “It is essential that our long-term investigations on the decline of native ladybird species are continued, as we need to know whether this decline will persist and whether some species are at risk of local extinction.”