A battle with a potentially devastating enemy at one of the world's finest cathedral's is being renewed.
The roof of Lincoln Cathedral, parts of which date back to the 11th Century, is infested with death watch beetle.
Larvae from the beetle bore into roof beams, seriously weakening them, and can live there for a decade.
After securing £300,000 in funding, experts have started cutting away the worst affected beams and treating others with a special pesticide.
The cathedral has an annual general maintenance bill of about £1.5m.
But the grant means work can be focused on the north-west transept triforium area, the aisle-level roof below the main roof, where lead has become worn and damaged.
Carol Heidschuster, cathedral works manager, said: "When water gets in, timbers begin to rot and the beetles just love that.
"In a situation like this we would never be able to eradicate the death watch beetle, the roof is just too large.
"The death watch beetle likes old decaying timbers and we will never be in a position where we put all brand new timbers in the roof.
"So there will always be death watch beetle in this building."
Work in this area is expected to take three years and cost around £1m.
Allan Toyne, from the cathedral works department, said the effects of the beetle can be dramatic.
"The eggs will be laid somewhere near a crevice where they will hatch and burrow in.
"They can be there for 10 years or longer depending on the climate and while they are in there they burrow around and in the worst cases, turn the wood to dust."
Not all of the funding for the work is in place and the cathedral is launching a second bid for Heritage Lottery funding after its first failed.