Blickling Hall reveals use of 'microwasps' to defend its treasures

The National Trust has said the trial - which has seen microscopic parasitoid wasps introduced to lay eggs inside the moths' own eggs - has proven a success since its launch a year ago, cutting moth numbers by 83pc at the historic building.

Hilary Jarvis, the trust's assistant national conservator who is responsible for putting together an annual 'pest report', said the reopening of Blickling and other sites had also helped quell a boom in insect pests seen during lockdown.

Ms Jarvis said: "There’s no doubt that lockdown was good for pests. Despite regular monitoring by our housekeeping teams, closure helped create the type of environment where pests and mould can settle and spread.

"As the review shows, it’s better for our houses to be occupied – busyness and activity play an important role in conservation.

"This isn’t just about staff vacuuming and opening and closing shutters and doors, it’s also about visitors who, without even knowing it, help drive all-important airflow."

House steward Ellie Hobbs records moth numbers caught on a pheromone trap, by the State Bed at Blickling. (Image: National Trust/Kenny Gray)

Ms Jarvis said at the trust's other properties, webbing clothes moth number had risen by 18pc - making them the most common insect pest they had to contend with.

The trials at Blickling have also used pheromones, which are designed to emulate the natural chemicals female clothes moths give off, confusing the males when it comes to mating time.

Ms Jarvis said: "The second year [of the trial] will be about establishing whether wasps and pheromones are better than pheromones alone. This will help us to protect our collections from moths in the most efficient way we can."

Exterior of the house at Blickling Estate, Norfolk. (Image: ©National Trust Images/ Ian Ward)

But she said climate change change also seemed to be having an effect on insect pest numbers.

Ms Jarvis said: "Our increasingly variable spring and summer weather is likely encouraging more or simply longer breeding cycles at different points of the year these days, meaning ‘normal’ may be a redundant concept.

"The warmer, wetter winters to which we’re increasingly accustomed are not just driving diseases in our landscapes, such as ash dieback, they’re also likely to be supporting the moths, spider beetles and booklice, not to mention the cluster flies whose eggs are clearly thriving in soils subject to fewer and fewer harsh frosts."

Among the miniature creatures on the move are ‘woolly bears’ - carpet beetle larvae that feed on silk, wool, fur and feathers - which appear to be moving into the North of England and Wales.

Ms Jarvis said: "The adults feed on nectar and pollen, so it could be that earlier springs and longer flowering periods are helping them to increase their range.

"Although it’s more likely linked to longer periods for larval development."

Another pest the trust has to contend with are cluster flies.

Although the flies are not themselves a threat to collections, they are a good food source for other insects, so can compound pest problems if not cleared up promptly – a task that can take busy house teams up to an hour a day.

Silverfish did less well than other insects in 2021, with recorded numbers slumping by 31pc. These consumers of books, paper and cotton are continuing their decline from a 2019 peak, possibly due to drier conditions overall across the year.

The tapestry from Catherine the Great is among the most valuable treasures at Blickling, and one of many which could be vulnerable to clothes moths.

Made around 1764, it depicts Peter The Great at the Battle of Poltava, and was a gift to Blickling's former owner, the Second Earl of Buckinghamshire, on the completion of his three-year spell as English ambassador to Russia.

Webbing, which indicates clothes moth activity on the back of a tapestry in the care of the National Trust. (Image: National Trust/Kenny Gray)

Damage to a sedan chair caused by moths at a National Trust property. (Image: National Trust/Kenny Gray)

Loss of pile in a carpet caused by webbing clothes moths. (Image: National Trust/Kenny Gray)

House steward Ellie Hobbs places a dispenser of parasitoid wasps near a tapestry at Blickling. National Trust_Kenny Gray (Image: National Trust/Kenny Gray)

Clothes moth frass (faeces) and webbing on carpet. (Image: National Trust/Kenny Gray)

Silverfish feasting on an old book at a National Trust property. (Image: Getty Images/iStockphoto)