Butterflies 'more endangered than tigers Previous international studies have focused on groups of animals such as mammals and birds. As invertebrates make up 97 per cent of species, the International Union for the Conservation of Nature, the UN body in charge of ensuring that animals do not become extinct, asked the society to lead a new study. More than 12,000 species, from giant squid to midges, were studied around the world. There are 1.5 million known invertebrates, although eight million species are thought to exist even if not yet discovered. Prof Baillie said scientists were shocked by the results. "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," he said. The initial findings in this report indicate that 20 per cent of all species may be threatened. The most threatened group are freshwater invertebrates because of the invasive signal crayfish from America. Dams and pollution from nitrates used in fertilisers on fields have also played a part. Marine species, including foods such as shrimp, squid and crab, are most at risk of ocean acidification, which threatens shell-building molluscs and coral. Insects on land are being driven out by human development such as cities and pollution caused by cars and factories. All species are in danger from further habitat loss caused by climate change. Prof Baillie said that invertebrates help store carbon at the bottom of the ocean, filter water, decompose waste, pollinate important crops and are an essential part of the food "web," ultimately feeding hundreds of millions of people. Even pests have a place in the ecosystem, he said. We ignore the loss of invertebrates at our peril, as they provide many of the ecosystem services from which humans benefit.