The dark rooms in Britain’s historic buildings are empty of visitors due to locks and have suffered thousands of unwelcome residents over the past 11 months: moths contaminating cupboards, sitting in beams and floorboards and nibbling on precious tapestries, furniture, carpets and art.
At a centuries-old estate, Blickling Hall in Norfolk, England, the charity that runs the sprawling grounds tries to stop the moths with an even smaller set of visitors: wasps.
The National Trust, the heritage and conservation organization, hopes to ward off the moths by sending thousands of microscopic wasps – measuring just 0.5 millimeters – that chop moth eggs.
“It’s not like our tapestries are falling off the wall and our belongings are being smashed to pieces,” said Hilary Jarvis, an assistant national conservator at the National Trust.
“It’s just that no harm is acceptable and that it’s heartbreaking when you find something,” she said. “We know they are there and that we are not going to be complacent, and I can not take the risk of the moths thriving.”
The plan is for a company that helps plague museums, Historyonics, to place the little wasps called Trichogramma. evanescens, on maps around the building. From there, they will seek out moth eggs to lay their own, which will stop the moth reproduction process.
The company will also try a second tactic of spreading a female moth pheromone to confuse the moths and reduce their chances of finding a mate.
The wasps, which are invisible to the human eye, pose no danger to humans, said David Loughlin, the manager of Historyonics. The insects live only about two weeks and once they are dead, their bodies disappear into household dust.
“They should not be confused with the wasps you sting when you have a picnic,” he said. ‘This is another point of the spectrum. It’s like comparing a domestic Chihuahua to a wolf. ‘
Blickling Hall, one of the more than 500 historic castles, houses, parks and monuments maintained by the National Trust, has a large collection of valuable items that the charity would like to protect.
Blickling, a 17th-century property with red bricks, sits on the foundations of a mansion that was presumably the birthplace of Anne Boleyn, the second wife of King Henry VIII (beheaded in 1536). A star of the hall’s collection is an 18th – century tapestry by Tsar Peter I of Russia, given by one of its former successors, Catherine the Great, to one of the building’s former owners.
The moth problem in the building has worsened for years, although the insects have so far done only minimal damage to its treasures.
The anti-moth campaign starts early next month and lasts through the rest of the year. The National Trust has previously used wasps and the pheromone technique separately for short periods of time, to varying degrees of success, but the charity will try both at Blickling for the first time.
The use of wasps to combat moth and other insect problems is a technique that is widely used in agriculture, especially in greenhouses, said James Kitson, research fellow for ecology and agriculture at Newcastle University in Britain. The measure works best in controlled environments and can work well inside the hall, he said.
The wasps are unlikely to leave the house because their entire and extremely short life cycle is aimed at finding a mate and a new host, said dr. Kitson said. “When these things get outside in the real world, they have to compete with hundreds and hundreds of species that do the same to other native moths in the area,” he added.
If the trial significantly reduces the moth population, Jarvis said it could be used in other charities experiencing the same problem.
A National Trust survey of the many properties found that the number of bugs increased by 11 percent in 2020 compared to the previous year, making a thriving insect population in Britain’s stately old homes one of the many unforeseen consequences of pandemic make connections.
The problem extends beyond Britain: around the world, buildings and roads that suddenly became quiet through home visits gave animals the chance to venture where they normally could not. Goats were expected to run through Welsh streets, coyotes wandered around San Francisco and bats lay between the walls of newly empty buildings in Austin, Texas.
“They want to take advantage of the gap,” said Lee Mackenzie, a co-founder of Austin Bat Refuge, a city-based rescue organization that is regularly called upon to evict bats. “They simply go, ‘Oh, nobody uses this space, nobody will mind if we go here.’ .)
The National Trust has also noted that mold outbreaks are a problem exacerbated by locks, a problem that many modern building owners also experience in offices not inhabited by the pandemic.
However, moths probably do not present a problem in offices, said Mr. Loughlin said. They mostly avoid the synthetic carpets used there.
Christine Hauser contribution made.