The number of worms, spiders, butterflies and other invertebrates has declined by 45 per cent on average over the past 40 years, threatening food supplies, human health, and water quality. The study, published on Friday in the journal Science, reviewed past studies, and compiled a global index of all invertebrate species. The researchers found that, while the human population has doubled over the past four decades, 67 per cent of the world’s invertebrates have decreased in numbers by an average of 45 per cent over the same period. In the UK, for example, there has been a 30 to 60 per cent decline in the number of butterflies, bees, beetles, and wasps. “We were shocked to find similar losses in invertebrates as with larger animals, as we previously thought invertebrates to be more resilient,” said Ben Collen of University College London, a co-author of the study. The fall in invertebrate numbers is thought to be linked to the loss of natural habitats. “The richness of the animal world of our planet is being seriously threatened by human activities”, said lead author Rodolfo Dirzo, a process he calls “anthropocene defaunation”. The experts warn that the decline in invertebrates could have serious effects on ecosystems and food production. 75 per cent of the world’s food crops rely on insect pollination. Moreover, invertebrates contribute significantly to agricultural pest control. The cost of pest control without natural predators could amount to more than $4.4 billion dollars in the United States alone. Insects, spiders, and worms also play a decisive role in decomposition, ensuring soils contain nutrients that are needed for plant growth. Invertebrates are also important for the natural purification of water, the study said.