Britain's food chain threatened by loss of one in five insect species

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A serious decline in the number of British insect species in the past few decades, with up to 20 per cent being lost in some parts of the country, has been uncovered by scientists.

A serious decline in the number of British insect species in the past few decades, with up to 20 per cent being lost in some parts of the country, has been uncovered by scientists.

Entomologists at Oxford University surveyed the records of insects in central England over the past 100 years to compare species seen today with those documented at the beginning of the last century.

They found that in Warwickshire, which has one of the most comprehensive set of records on insect sightings, many species of beetle, dragonfly, bee and butterfly have not been seen for many years.

Darren Mann, an entomologist at the University Museum in Oxford, said that Warwickshire was a good county to study because it was where the ranges of many northern and southern insect populations overlap.

"In Warwickshire we actually have about half the British fauna," Dr Mann told Radio 4's Today programme, which commissioned the survey.

Between 1904, when the county history was published detailing insect sightings, and 1960, about 15 per cent of insects had disappeared. The loss has since accelerated, with 20 per cent being lost. "So that means one in five British insects has not been seen since 1960," Dr Mann said.

One of the most famous examples is the disappearance of the large blue and the large copper butterflies, both common in Victorian times. Ground beetles, crickets and dragonflies have also suffered, especially those living in threatened habitats, such as wetlands and ancient woodlands.

George McGavin, the assistant curator at the museum, said the insect decline was a cause of concern because they formed the basic links in a complicated food chain ending in higher animals including humans. Dr McGavin said: "The problem is that insects are small so the majority of individuals tend to overlook them. In terms of how ecosystems function, insects are vital.

"Energy from the Sun makes plants grow, insects eat plants, other insects eat them and eventually you reach larger animals. Basically ecosystems and food chains rely on small things at the grass roots. If you take them away, everything collapses."

Of the 267 species of bee living in Britain, about a quarter are threatened with at least one species of bumble bee having disappeared altogether, said Chris O'Toole, a bee specialist at Oxford. Dr O'Toole said: "Every third mouthful of our food is directly dependent on the unmanaged pollination services of our bees.

"Without bees whole ecosystems will collapse and we are seeing that now."

There are 22,000 insect species recorded in Britain, which has one of the best described insect populations in the world, with records going back 250 years. Insects have come and gone many times over the 12,000 years since the glaciers retreated from the British Isles but the recorded decline over the past 100 years appears to be part of a more serious trend.

Peter Hammond, a research entomologist at the Natural History Museum in London, said: "There has been a selective decline and we should be worried about it."

The main reason for the recent loss of insects seems to be the drastic changes in land use, from the draining of the Fens and the Somerset levels to the digging up of hedgerows and replanting of deciduous woodlands. Dr Hammond said: "If you chop down an oak forest and replace it with spruce conifers the balance of the equation is almost certainly a loss of species."

Chemical insecticides had also contributed to the decline, although less so than the loss of natural habitats, he said.