By Helen Briggs
BBC News science reporter
The British moth population is in rapid decline, according to the most comprehensive study of its kind.
A report by Butterfly Conservation says the number of common moths has fallen by a third since 1968.
This has serious implications for animals such as birds and bats which feed on moths, says the UK charity.
It also raises concerns about the state of Britain's natural heritage since moths are an important indicator of biodiversity.
"It's very bad news indeed," said study author Richard Fox. "Moths are a huge group; they are a really significant part of our biodiversity.
"If we are finding these declines amongst such a major group as the moths, then it is a very, very clear signal that British biodiversity as a whole is suffering similar rates of decline."
The Butterfly Conservation report focussed on Britain's larger moths - 337 species that are regularly captured and studied at hundreds of sites across the UK.
Much of the data came from a nationwide network of moth traps maintained since 1968 by the scientific institute Rothamsted Research.
The report found that:
Scientists have yet to pinpoint why moth numbers are falling so rapidly; but they say habitat destruction, pesticides, pollution and climate change are the main suspects.
- The number of larger moths in Britain has decreased by 32% since 1968
- Two-thirds of the 337 moth species studied showed a decreasing population trend over 35 years
- More species have declined in southern Britain (75%) than in northern Britain (55%)
- Under the international (IUCN) criteria, 71 species (21%) of these common moths are threatened.
"Whatever is causing the declines must be something that is affecting the whole of our country," said Richard Fox.
"They are not subtle things that are affecting a few rare species; these are big scale changes and they are obviously going to need big scale changes to reverse them."
Climate change is likely to be having an impact on moths, he said, since temperature governed the lives of many insects.
"Even though we don't have the evidence that we would like yet, I have no doubt that climate change will be affecting many of these species," he told the BBC News website.
Dr Martin Warren, chief executive of Butterfly Conservation, said the data was highly significant because it was the first to show how widespread the decline was in insects.
"If other insects are declining at the same rate - and we have no evidence to believe any different - then we are really going through a big biodiversity crisis, and we've only just seen the tip of the iceberg," he said.
He added there needed to be a change in government policy to provide better resources for conservation in the town and countryside.
"The fact that it's on-going is very worrying so there's a huge amount of work to be done to conserve biodiversity."
Butterfly Conservation's president Sir David Attenborough said he hoped the report would spur a concerted action to save moths, not just for themselves, but for the many species that depended on them and shared their habitat.
"Nobody else can provide the continuity of observations and records of moths and butterflies compared with what's been done in Britain," he told the BBC News website.
"And it's that look back to see what the trends have been which enables us to see what's likely going to happen in the next few years."
Images courtesy of Butterfly Conservation.