Britain's Zoological Society, conducting the biggest study of invertebrates ever done, found one in five species is at risk of dying out.
Invertebrates such as slugs and snails may not have the charisma of lions or dolphins but are just as important to providing the food we eat and the countryside we love, one researcher said.
"These critters form the basis of many of the essential benefits that nature provides; earthworms recycle waste nutrients, coral reefs support a myriad of life forms, and bees help pollinate crops," Jonathan Baillie, director of conservation at the Zoological Society, told The Daily Telegraph.
"If they disappear, humans could soon follow."
More than 12,000 species of invertebrates, from giant squid to tiny insects, were studied around the world, the researchers said.
There are 1.5 million known invertebrates, although 8 million species are thought to remain to be discovered.
Scientists said they were shocked to discover so many invertebrate species threatened with extinction.
"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," Baillie said. "The initial findings in this report indicate that 20 percent of all species may be threatened.
"We ignore the loss of invertebrates at our peril, as they provide many of the ecosystem services from which humans benefit."
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