NUMBERS of insects and other invertebrates such as spiders, crustaceans and worms have nearly halved in 35 years as the human population has doubled, a study warns.

The decline in invertebrate numbers mirrors similar reductions elsewhere in the animal kingdom as humans have triggered catastrophic disasters and population declines that have put the world into a "sixth mass extinction".

Around two thirds of monitored invertebrate species have seen a decline in numbers of 45 per cent on average, the study published in the journal Science said.

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The falls in invertebrate numbers came as a surprise to scientists, who had thought they were more resilient than larger species such as birds and mammals.

Their decline poses a major problem as they help provide important services in the natural cycle from pollination and pest control for crops to water filtration and breaking down plant and animal matter to return nutrients to the ground.

The scientists, led by University College London and Stanford and UCSB in the US, said the decrease in invertebrate numbers was due to two main factors - habitat loss and increasingly the impact of disruption to the climate.

Dr Ben Collen, from UCL, said: "We were shocked to find similar losses in invertebrates as with larger animals, as we previously thought invertebrates to be more resilient. We are in the potentially dangerous position of losing integral parts of ecosystems without knowing what roles they play in it."