Millions of very hungry ladybirds are poised to create ecological havoc for hundreds of Britain's native species, scientists warn today.

Experts said the anticipated warm summer would provide the perfect conditions for the Asian harlequin ladybird to breed and prepare for a springtime assault. "They are creating a huge genetic stock ready for next year," said Helen Roy, a scientist with the Centre for Ecology and Hydrology.

The insect, a voracious predator, has spread across the UK since its arrival from continental Europe in 2004. The bugs have been spotted as far north as Orkney, though they remain strongest in south-east England, where they have overrun many of London's parks.

"We believe that the negative impacts of the harlequin on Britain will be far-reaching and disruptive, with the potential to affect over a thousand of our native species," she said. "It's a big and voracious predator, it will eat lots of different insects, soft fruit and all kinds of things."

Unlike British ladybirds, such as the most common seven-spot, the harlequin does not need a cold winter for adults to reach sexual maturity, and so be able to breed. "That gives them a massive advantage," Roy said.

The ladybird, originally from Asia, was introduced to Holland and other European countries to control aphids on crops. From there, it crossed the English Channel on the wind, or hidden on fruit and flowers.

A public survey launched in 2005 has tracked its progress using some 30,000 online records. Roy said the results revealed a "staggering expansion". Scientists fear the harlequins will push out natural rivals through competition for food. They can munch through more than 12,000 aphids a year, as well as feed on other species such as lacewing larvae. The harlequin has even been recorded eating the large caterpillar of a brimstone butterfly.

Scientists from five organisations will present the latest findings on the spread of the harlequin this week at the Royal Society summer exhibition, and warn its arrival will mean "one winner, 1,000 losers".

Scientists are exploring whether harlequin numbers could be controlled using their few native enemies, such as fungal disease, male-killing bacteria and parasitic wasps and flies. One idea is to encourage the transmission of a sexually transmitted mite that makes some ladybirds infertile.

The researchers said people should not take matters into their own hands. Vigilante action against the harlequin invaders would make no difference to the overall population and could inadvertently kill similar-looking native species.