The march of the insect invaders

By Rebecca Morelle Science reporter, BBC News

Alien insects are having a dramatic impact on the UK's native flora and fauna.

Some have been deliberately introduced, while others are hitching a ride into the UK on imported plants and food.

Here are some of the key insect invaders that are causing ecologists concern.

The harlequin ladybird (Harmonia axyridis), which comes from Asia, was first introduced to Europe to control the spread of aphids on crops.

However, it rapidly spread, and arrived in Britain in 2004.

See distribution of harlequin ladybird Enlarge Map

The species is an extremely voracious predator that outcompetes the UK's native species and even feeds on them.

Peter Brown, from the Centre for Ecology and Hydrology who co-ordinates the Harlequin Ladybird Survey, said: "Our surveys have shown that harlequin ladybirds are spreading extremely quickly and are causing a lot of damage to our native species."

To help scientists monitor the spread of the ladybirds, visit the Harlequin Ladybird Survey's website.

The oak processionary moth (Thaumetopoea processionea), a native species of central and southern Europe, can be found around London.

It is causing ecologists much worry - its caterpillars feed on the foliage of many species of oak, causing considerable damage.

However, it also poses a risk to human health. Silky hairs on the caterpillar contain a toxin, and contact or inhalation can cause severe skin irritation and allergic reactions.

Professor Monique Simmonds, from the Royal Botanic Gardens Kew, said: "This is a real potential pest."

Suspected sightings of oak processionary caterpillars or their nests in spring or early summer can be reported to the Forestry Commission's Forest Research agency.

Reports of the moths are not required because they are very difficult to distinguish from other similar moth species.

The rosemary leaf beetle is an attractive insect with metallic green and bronze stripes.

See rosemary leaf beetle distribution in England, Scotland and Wales Enlarge Map

But despite its good looks, this native of central Europe has been causing a problem for gardeners since it invaded the UK in 2003.

It has become a pest on rosemary, lavender and related plants, where it strips the leaves.

Andrew Salisbury, from the Royal Horticultural Society, said the insect was first spotted in the RHS gardens in Wisley, Surrey, but has now spread around the UK.

He is currently monitoring the species' movements. If you have spotted the beetle, you can help by submitting a record of your sighting to the Royal Horticultural Society.

The horse chestnut leaf miner (Cameraria ohridellais) is another recent addition to the UK.

See distribution of horse chestnut leaf miner in England and Wales Enlarge Map

After spreading throughout Europe, it was thought to have became established here in 2002.

Larvae of the tiny insect, which belongs to the moth family, burrow into the leaves of horse chestnut trees, creating unsightly brown mines.

Scientists are still unsure whether the moths are damaging the trees, but some believe the insects may leave the trees more susceptible to other pests.

The RHS's Andrew Salisbury describes the red lily beetle as "the lily growers' nemesis".

See distribution of red lily beetle Enlarge Map

This pretty insect, which is native to Eurasia, was first noted in the British Isles at the end of the 19th Century.

However, it has only been in the last decade where it has really started to spread.

Adults and larvae can devour a plant in a matter of days.

To help scientists keep track of the red beetle, you can submit a sighting to the RHS team.

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