Ground breaking new pest control trial at Blickling Hall

House Steward Ellie, cleans the State Bedroom carpet

Moth hole in Blickling's Brown Drawing Room carpet

Published : 17 Feb 2021 Last update : 01 Apr 2022

Despite vigilant housekeeping and other preventive measures, common or 'webbing' clothes moths have proved hard to control at Blickling Hall. In February 2021, the house team started a ground breaking new pest-control trial to tackle these moths, using natural methods, not previously used together in a heritage setting.

The plan

This multi-pronged trial uses a microscopic parasitoid wasp, Trichogramma evanescens, together with moth pheromones and the Trust’s existing regime, to target the whole lifecycle of the moth (adult, larva and egg), which can cause serious damage to carpets, furniture, clothing and other wool and silk objects.

The team are working in 11 key spaces of the hall, including the Long Gallery, Chinese Bedroom, Brown Drawing Room and Peter the Great Room. These 11 spaces are responsible for 80% of the total moth count.

Moth damage to the State Bedroom carpet at Blickling — Moth damage to the State Bedroom carpet

Parasitoid wasps

These wasps (barely visible to the human eye) are a natural enemy of the clothes moth (Tineola bisselliella), searching out moth eggs and laying their own eggs inside, so that a new beneficial wasp hatches, rather than a moth larva. Once the wasp eggs are laid, the wasps die naturally and disappear inconspicuously into house dust.

Pheromone ‘tabs’

These work continuously to spread female pheromones (chemicals released to attract members of the same species) which confuse male moths, reducing their chance of finding a female mate. The tabs use electrostatic technology to physically transfer the pheromone onto the bodies of male moths, turning them into portable female pheromone dispensers.

Phase 1

The trial started in 2021, at a time when the Trust found that insect pests such as moths and silverfish had thrived during lockdown, with fewer house staff and visitors to disturb them. Mild winters and warm springs have also helped push pest numbers to record levels. 2,455 moths were recorded in 2020 at Blickling.

An adult clothes moth, Tineola bisselliella

Results after year one of the trail

The trial is showing promising results. The pheromone and wasp combination has achieved a drastic 83% reduction in moth numbers, helping safeguard the hall’s precious collections, including a tapestry gifted to the estate by Catherine the Great in the 1760s.

" The second year 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."

Phase 2

The second phase of the moth trail started in March 2022. We will continue to use the wasps and pheromone tabs, but will introduce new control zones to further test the efficacy of each product and enhance our understanding.

A microscopic parasitoid wasp, barely visible to the human eye

Close view of part of carved armchair, late 18th century, giltwood and gesso, from the Drawing Room at Ickworth

Think like a bug and win the battle against household insect pests

Insects are essential to our ecosystem, indoors and out, but not so welcome when flying out of wardrobes or eating your favourite woolly jumper or carpet. What can you do? Hilary Jarvis, one of the National Trust’s Assistant National Conservators, shares some tips based on the latest findings and methods used in our historic houses to protect our collections, and reveals the most common pests of 2021.

The story so far...

23 Feb 21

Microscopic wasps

Since our announcement, we’ve had a great deal of interest in our pest-control trial, which has been in development for 12 months, drawing on the expertise of House Stewards, Preventive Conservators and an external expert. The wasps are harmless to humans and other animals and have been used successfully for many years in other settings. With a very limited range they are unlikely to move beyond the room they are released into. They have a very short lifespan, surviving only two weeks as an adult and naturally die once they have laid their eggs. They are a native species, known in the UK for nearly 140 years, so they already have a place in our ecosystems.

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