Empty of human visitors because of blockades, the dark rooms of Britain’s historic buildings have gained thousands of unwanted residents in the past 11 months: moths that infest cabinets, perch on beams and floorboards and nibble on valuable tapestries priceless, furniture, carpets and art.
On a century-old property, Blickling Hall in Norfolk, England, the charity that runs the extensive gardens is trying to stop the moths with an even smaller group of visitors: the wasps.
The National Trust, the heritage and conservation organization, hopes to ward off moths by sending thousands of microscopic wasps – each measuring just 0.5 millimeters – that sequester the moths’ eggs.
“It’s not like our tapestries are falling off the wall and our stuff is being destroyed,” said Hilary Jarvis, assistant national conservative at the National Trust.
“It turns out that no harm is acceptable and it is painful when you find something,” she said. “We know they are there and we are not going to be complacent, and I cannot risk letting these moths thrive.”
The plan is a company that helps museums with pests, Historyonics, to place the tiny wasps, called Trichogramma evanescens, in letters scattered around the building. From there, they will look for moth eggs to place their own inside, interrupting the moths’ reproduction process.
The company will also try a second tactic, spreading a female moth pheromone to confuse males and reduce their chances of finding a partner.
Wasps, invisible to the human eye, pose no danger to people, said David Loughlin, manager of Historyonics. Insects live only about two weeks, and when they die, their bodies almost turn into domestic dust.
“They shouldn’t be confused with the wasps that sting you when you’re having your picnic,” he said. “It is a different end of the spectrum. It is like comparing a domestic Chihuahua to a wolf. “
Blickling Hall, one of more than 500 castles, houses, parks and historic monuments maintained by the National Trust, has a large collection of valuable items that the charity is eager to protect.
Blickling, a 17th-century red-brick property, sits on the foundations of a mansion believed to have been the birthplace of Ana Boleyn, the second wife of King Henry VIII (beheaded in 1536). A star in the salon’s collection is an 18th century tapestry by Tsar Peter I of Russia, given by his successor, Catherine the Great, to one of the building’s former owners.
The building’s moth problem has worsened for years, although insects have done minimal damage to the treasures so far.
The anti-moth campaign will start at the beginning of next month and will continue for the rest of the year. The National Trust had previously used wasps and the pheromone technique separately for short periods, with varying success, but the charity will try both together for the first time in Blickling.
Using wasps to control moths and other insect problems is a technique widely used in agriculture, especially in greenhouses, said James Kitson, an ecological and agricultural researcher at the University of Newcastle in Britain. The measure works best in controlled environments and can work well inside the corridor, he said.
Wasps are unlikely to leave the house, as their entire extremely short life cycle focuses on finding a mate and a new host, Kitson said. “When these things go out into the real world, they have to compete against hundreds and hundreds of species that are also doing the same things with other moths native to the area,” he added.
If the test significantly reduces the moth population, Ms. Jarvis said it could be used on other charity properties with the same problem.
A National Trust survey of its many properties found that the number of insects increased by 11 percent in 2020 compared to the previous year, making a thriving insect population in Britain’s old mansions one of the many unforeseen consequences of pandemic blocks. .
The problem extends beyond Britain: all over the world, buildings and roads suddenly silenced by orders to stay at home have given animals the chance to venture where they normally could not. Goats were seen running through the streets of Wales, coyotes roamed San Francisco and bats nestled in the spaces between the walls of newly empty buildings in Austin, Texas.
“They want to take advantage of the void,” said Lee Mackenzie, co-founder of Austin Bat Refuge, a rescue organization in the city that is often called upon to expel bats. “They just say, ‘Oh, nobody is using this space, nobody will care if we go here.’” (Bats, like wasps, are sometimes recruited as pest control cavalry to get rid of unwanted insects, like those that damage plantations.)
The National Trust has also seen outbreaks of mold as a problem compounded by roadblocks, a problem that many modern building owners also face in offices that were left unoccupied by the pandemic.
Moths, however, are probably not a problem in offices, said Loughlin. They mostly avoid the synthetic rugs used there.
Christine Hauser contributed reports.