Almost one-fifth of Europe’s wood beetles are at risk of extinction due to a widespread decline in ancient trees, according to a new report which suggests their demise could have devastating knock-on effects for other species.

The study says 18% of saproxylic beetles – which depend on dead and decaying wood for some of their lifecycle – now exist on a conservation plane between “vulnerable” and “critically endangered”.

Another 13% of the insects are considered “near threatened” and their disappearance could have a disastrous impact on biodiversity and ecosystems, according to the new red list released by the International Union for the Conservation of Nature (IUCN).

Wood beetles are a key food source for small mammals, bats and for birds such as woodpeckers, nut hatchers and treecreepers. Some species are also pollinators.

Dr Keith Alexander, an ecological consultant who contributed to the report, told the Guardian: “Saproxylic beetles are intimately tied to everything else in the places where they occur. If you start to erode the varieties of life, then the ecosystem heads towards collapse.”

“In western Europe, there are already lots of intensively cultivated places where the fauna is incredibly poor compared to what it should be. We expect that things have started to unravel in these places, which have been simplified by people removing dead wood and changing the habitat’s whole structure.”

Healthy and varied wood beetle populations need large volumes of dead and decaying wood. Some species will only lay their eggs in hollow cavities containing mould that takes hundreds of years to form.

Logging and tree loss is “by far” the greatest menace to their way of life, the IUCN report says. But they also face a staggering array of threats, from urbanisation and tourism to arable farming, pollution and climate change.

One of the most avoidable hazards confronting wood beetles is the rigidity of the EU’s common agricultural policy’s (CAP) payment system, according to Luc Bas, the IUCN’s Europe director.

“It is critical for the CAP to promote the appropriate management of wood pasture habitats containing veteran trees across Europe,” he said.

“Currently, management practices lead to the transformation of wood pastures into either woodland or grassland, destroying the essential vegetation mosaic many saproxylic beetles need.”

The European commission funded the IUCN paper, which assessed 700 species of beetle, and was increasingly engaging with the effects of its CAP policies, Alexander said.