The National Trust has announced a new pest-control trial using natural methods, amid concerns that lockdown closures and fewer staff on site have created ideal conditions for moths to thrive.
The trial will take place at Blickling Hall in Norfolk, believed to be the birthplace of Anne Boleyn, where common or webbing clothes moths are a threat to areas of the collection such as the Peter the Great tapestry, gifted by Catherine the Great in the 1760s, and a state bed featuring a counterpane that is likely to be one of only two surviving pieces of Queen Anne’s throne canopy.
The trust is now launching a multi-pronged trial to tackle the issue. Alongside the property’s existing regime, it will release microscopic parasitoid wasps, which are non-harmful to humans and lay their eggs in moth larva.
Measuring about 0.5mm, the wasps are supplied in small card dispensers containing around 2,400 wasps that can be discreetly hung or placed in drawers or open rooms. Once the eggs are laid, the wasps die and disappear into house dust.
The trust is also planning to use specially prepared moth pheromones tabs to disrupt adult moth mating. These work continuously to spread female pheromones, confusing male moths and reducing their chance of finding a mate. The tabs use electrostatic technology to physically transfer the pheromone onto the bodies of male moths, turning them into portable female pheromone dispensers.
While wasps and pheromones have been used separately against clothes moths, and pheromones have been used to manage moth pests in agricultural settings, the National Trust says the combination hasn’t been deployed in a heritage setting until now.
Hilary Jarvis, the National Trust’s assistant national conservator, says: “We are really hoping this pioneering approach will provide a practical and sustainable method that any of our properties can use to deal with serious infestations.
“Although these are rare, they can sometimes prove immune to our usual, more gentle approaches, with potentially serious results.”
Results from the trial are not expected until autumn at the earliest, but the trust hopes to share initial findings at the Pest Odyssey virtual conference in September.
Pests such as moths and silverfish are believed to have thrived since last March, partly due to Covid lockdowns meaning less disturbance from house staff and visitors.
“There’s no doubt lockdown suited our resident bugs,” Jarvis said. “The relative quiet, darkness and absence of disruption from visitors and staff provided perfect conditions for larvae and adults alike from March onwards.”
The trust’s annual pest review saw a 3% rise in webbing clothes moths, alongside an 8% fall in silverfish probably due to warmer weather. Analysis shows that insect numbers rose overall by 11% in 2020 compared to 2019, with many houses also reporting mould outbreaks, due to a lack of activity to drive airflow.