Facing disaster: the little things that rule the world

One-fifth of the world's invertebrates, "the little things that run the world," may be heading for extinction, according to the Zoological Society of London.

The society (ZSL) suggests that about 20 per cent of the world's insects, spiders, worms, crustaceans, molluscs and other animals without backbones are endangered, for reasons ranging from pollution and over-harvesting to the effect of invasive species.

The report, entitled "Spineless", and produced in conjunction with the International Union for Conservation of Nature (IUCN), which compiles the Red List of threatened species, is the first attempt at estimating the global conservation status of invertebrates.

Invertebrates constitute almost 80 per cent of the world's 1.9 million known species and display staggering diversity, ranging from microscopic zooplankton to giant squid which can reach 18 metres in length.

But much less attention is paid to them than to vertebrate animals, which include mammals, birds, fish and reptiles, and are far fewer in number (totalling about 60,000 species).

And this is the case even though invertebrates are crucial in maintaining ecosystems – without insects, for example, we would lose much of the pollination services upon which agriculture depends, and without earthworms, the processes that spread organic matter through soil would be disrupted.

Two years ago, an earlier study suggested that a fifth of all vertebrates were facing extinction, and today's report puts the conservation status of the smaller and more numerous invertebrate animals at the same level.

Threatened species in Britain include the brilliantly-coloured ladybird spider, once thought extinct and clinging on in Dorset and the freshwater pear mussel, famous for its pearls and now confined to a handful of rivers. Also at risk is the white-clawed crayfish, which has been ousted from many of its haunts by an American crayfish species. Others at risk in the UK include the shrill carder bee, the tansy beetle and the bog hoverfly, found only on Dartmoor.

The new report was carried out by analysing the 12,000 invertebrate species whose conservation status has been investigated and assessed by the IUCN, and projecting the threat across all species. It found that the highest risk of extinction tends to be associated with species that are less mobile and are only found in small geographical areas.

For example, vertebrate amphibians and invertebrate freshwater molluscs both face high levels of threat – around one third of species. In contrast, invertebrate species which are more mobile like dragonflies and butterflies face a similar threat to that of birds, and around one tenth of species are at risk.

"Invertebrates constitute almost 80 per cent of the world's species, and a staggering one in five species could be at risk of extinction," said Dr Ben Collen, of the ZSL.

The society's director of conservation, Professor Jonathan Baillie, added: "We knew that roughly one fifth of vertebrates and plants were threatened with extinction, but it was not clear if this was representative of the small spineless creatures that make up the majority of life on the planet.

"The initial findings indicate that 20 per cent of all species may be threatened. This is particularly concerning as we are dependent on these spineless creatures for our very survival."

At risk: Bugs' lives

Bog hoverfly (Eristalis cryptarum)

A rare hoverfly that in recent years has been found only within a restricted area of Dartmoor.

Shrill carder bee (Bombus sylvarum)

Threatened by loss of the extensive flower-rich areas and suitable nesting sites of long tussocky grass it needs to survive.

Freshwater pearl mussel (Margaritifera margaritifera)

Facing threats from illegal pearl fishing – 75 per cent of the species' sites have been damaged by criminals.

Tansy beetle (Chrysolina graminis)

Once widespread, but dependent for its sole food source on the tansy plant, which is declining.