Clothes moths retreating at National Trust properties, survey shows

An alarming increase in the clothes moth population in National Trust (NT) properties appears to be reversing, with the pest’s numbers plummeting in 2022.

The trust, which monitors the presence of insect pests every year, said it was surprised by the results of the 2022 survey. Total insect counts decreased by 3% compared to 2021, but the number of insects decreased Tineola bisselliella fell 39%.

Clothes moths can cause serious damage to carpets, upholstery, taxidermy and woolen or silk items. The larvae feed on protein in animal-based fabrics such as wool, fur, velvet and silk before becoming winged insects.

The NT monitors 6,500 sticky traps placed in 180 properties each year. The traps are checked four times a year, with staff and volunteers counting and classifying thousands of insects.

Hilary Jarvis, the trust’s assistant national conservator, who compiles the annual pest report, said the drop in clothes moth numbers after an 18% rise in 2021 was “surprising news”.

“We thought that climate change would help this elm, which comes from South Africa and is no stranger to heat.

“But changing weather patterns are challenging our thinking. Was it simply too hot – and perhaps more importantly too dry – for these particular moths to thrive in the hottest year on record?”

Other factors may include natural correction and increased efforts by house staff to control the infestation, including the use of pheromones.

During the Covid lockdown, when NT properties were closed, the insect population increased, Jarvis said. “Everything was closed, there were no visitors, there was no dusting. The numbers really rose. The most important thing is not to let them get too comfortable.”

Despite the overall drop in the number of insect pests, silverfish (Lepisma saccharina) jumped 14% to the No. Whitefish feed on books, paper and cotton.

Many NT homes also reported high numbers of “woolly bears” – carpet beetle larvae, which feed on silk, wool, fur and feathers. Bookworms and the Australian spider beetle were among the five most prevalent insect pests last year.

The trust takes a preventative approach to insect pests, including dust removal and maintaining environments that are not too hot or too humid. He uses an insecticide if necessary.

They have decided to end a trial at Blickling Hall in Norfolk using it Trichogramma micro-parasitic bees that lay their own eggs inside moth eggs.

“The micro-bees were very successful in terms of reducing the number of moths in combination with pheromones, but nothing was better than where we used pheromones alone,” said Jarvis.

“With so many potential drivers of insect activity, it’s not easy to predict what will happen next with clothes moths or any other insect pest. Our main job is to keep robust records of the normal insect profile of our homes, so that we can be alert to changes and potential risks, and be ready for action.”

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