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

The decline in invertebrate numbers mirrors similar reductions in the abundance of other animals as humans have triggered extinctions, threats and population declines that 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. 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 from pollination and pest control for crops to water filtration and breaking down plant and animal matter to return nutrients to the ground.

Some three-quarters of all the world’s food crops are pollinated by insects and pollination is worth around 10 per cent of the economic value of the world’s entire food supply.

But globally, pollinators appear to be strongly declining in both numbers and variety.

The scientists, led by University College London (UCL) 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.

In the UK alone, areas inhabited by common insects such as beetles, butterflies, bees and wasps saw a 30 per cent to 60 per cent decline over the last 40 years, the scientists said. 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.

“While we don’t fully understand what the long-term impact of these declining numbers will be, currently we are in the potentially dangerous position of losing integral parts of ecosystems without knowing what roles they play within it.

“Prevention of further declines will require us to better understand what species are winning and losing in the fight for survival and from studying the winners, apply what we learn to improve conservation projects.

“We also need to develop predictive tools for modelling the impact of changes to the ecosystem so we can prioritise conservation efforts, working with governments globally to create supportive policy to reverse the worrying trends we are ­seeing.”