Alien ladybirds 'spell disaster' for British species

The threat from one of Britain's most damaging invasive species has taken a giant step forward.

Harlequin ladybirds, voracious insects from Asia which seriously threaten Britain's ladybird species, and arrived in the UK two years ago, have begun forming big swarms for the first time, showing how their population has started to explode.

Thousands of the insects have come together in clouds on the south coast of the Isle of Wight, smothering vegetation and covering outside walls and window frames.

At the end of last week walkers reported thousands more clogging up footpaths on the picturesque Compton Down. Some people have been forced to use vacuum cleaners to suck up the insects in their homes.

The arrival of the harlequin, which has killed many insects in the US and other countries where it was mistakenly introduced as a pest control, was labelled a "disaster" by Britain's principal ladybird expert, Michael Majerus, of the genetics department at Cambridge University.

Dr Majerus predicted that Harmonia axyridis would outcompete most of Britain's 46 native ladybird species for their principal food - aphids - or prey on their eggs and larvae, and when it had eaten all the aphids it would eat other insects such as hoverflies, lacewings and butterflies, their eggs and their larvae.

The swarms on the Isle of Wight were thought by local ecologists to have migrated across the Channel from the Continent.

But Dr Majerus's research student, Remy Ware, who is studying for a PhD on the effects of the harlequin on Britain's ladybirds, said it was likely that their presence in such large numbers had a more damaging reason: the cold snap of last week had encouraged insects which were already here to go into their winter swarming behaviour.

"It's unlikely to be a mass migration from the Continent," she said, "It's more likely to be them looking for an over-wintering shelter."

Ms Ware said that when the insects swarm in this way, they go beyond being a threat to other wildlife and become serious pests, not only for agriculture but also for people.

"In the US there are reports of them covering the whole sides of people's houses," she said. "When you disturb them to try to get rid of them, they give off a yellow substance known as reflex blood which is foul-smelling and unpleasant, and can stain carpets and furniture."

The harlequin has been known in the Isle of Wight only since last year, Ms Ware said, so its ability to swarm already was an indicator of how rapidly its population was growing. "This is a significant event," she added.

The harlequin, which can be a variety of colours but is often orange with black spots, is bigger than nearly all of Britain's ladybird species.

Originally from Asia, it was introduced as a biological control of aphids and scale insects in the US in the 1980s, but spread alarmingly to become a pest itself.

In the past decade its huge increase in numbers has threatened endemic North American ladybirds and other aphid predators, many of which are plummeting alarmingly in their numbers as the harlequins consume their prey.

Now, it poses a dire threat to many of Britain's species such as the familiar seven-spot ladybird. It has been in the UK since only September 2004, when the first insect was spotted in Essex - and thought to have arrived here from the Netherlands, where it was also used as a biological control.

Yet it has already spread as far as Nottingham and Staffordshire, according to Ms Ware, who is helping to conduct a survey on the insects' progress.

The survey can be accessed at www.harlequin-survey.org.