The number of butterfly and moth species migrating to Britain for the summer has increased fourfold in the past 25 years, researchers have found.

With each degree of temperature rise resulting from global warming, 14 extra species can be expected to cross the English Channel in search of new breeding territory.

Many will end up staying permanently — as 89 species of moth have already done over the past century — rather than migrate annually.

But while some visitors may be a delight to the eye, there are fears that they could drive out native species and bring disease with them.

Butterflies and moths represent only a small proportion of the insect immigrants, said Tim Sparks, of the Centre for Ecology and Hydrology in Monks Wood, Cambridgeshire, who led the study. Others that could arrive here include malaria- carrying mosquitoes.

“Insect migration is a topic of great importance. It has implications for human health and agrarian economics, as well as conservation,” Dr Sparks and his team of researchers report in the European Journal of Entomology.

“Migratory species may be among the most adaptable. For this reason they may represent a competitive threat to resident species, which typically have lower mobility and are more specialised in habitat requirements. They introduce species hosting infections and disease to new regions. They can also have a serious impact on essential crops and garden plants.”

The study analysed records of lepidoptera seen since 1982 at the Portland Bird Observatory in Dorset, and found that the average number of migrant species has increased from ten to forty a year.

Seventy-five types of butterfly and moth are known to migrate to Britain, though only two — the convolvulus hawk moth and the dark sword-grass moth — are seen every year.

Frequently visiting butterflies include clouded yellows, red admirals and painted ladies. The first two are still regarded as migrant species, despite some limited over- wintering in Britain. Long-tailed blues and the monarch are among the rarer visitors.

Migrant moths include the hummingbird hawk moth, the hoary footman and the small thistle. Some are pests, including the gypsy moth, whose caterpillars can devastate forests by stripping trees of their leaves. Dr Sparks said: “This report confirms what we have been anticipating; that Britain will gain an increasing number of migrant insects from southern Europe as the climate warms.

“We have plenty of evidence for changing migration patterns in birds, and now, for the first time, we have confirmed similar patterns for this important group of insects. The possible consequences . . . require immediate attention.”

Less welcome

Gypsy moth
Voracious caterpillars defoliate trees

Leaf-mining moth
Attacks horse chestnuts

Oak processionary moth
Damages oak trees and causes allergic reactions in human beings

Colorado beetle
Can destroy potato crops

Allium leaf miner fly
Attacks onions and chives

Red lily beetle
Eats fritillaries

Rosemary beetle
Eats rosemary, lavender and thyme

Harlequin ladybird
Feared to be driving out native ladybirds

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