Wet winter causes rise in silverfish and woolly bears - Museums Association

Wet winter causes rise in silverfish and woolly bears

National Trust warns turbulent weather is blurring traditional pest breeding periods
National Trust pests
A member of National Trust staff cleans a book in the library at Ham House and Garden in Surrey
A member of National Trust staff cleans a book in the library at Ham House and Garden in Surrey Chris Davies

The National Trust’s annual insect pest report has found an 11% fall in overall pest numbers across its properties, with numbers of the dreaded clothes moth falling 18%.

But the wet winter has seen a rise in “damp-loving” silverfish, whose numbers rose by 6%. The trust warns that earlier springs and milder autumns are blurring traditional breeding peaks into “one long reproductive season”.

“This slight rise [of silverfish] does coincide with the UK becoming wetter over the past few decades,” said the trust’s assistant national conservator Alexandra Radford, who compiled the report.

“While we aren’t necessarily getting more rain, incidents of heavy rainfall have slightly increased. These more intense periods of rainfall can lead to water run-off and flooding, and we know silverfish will seek out and thrive in damp environments.” 

Also on the rise are woolly bears (carpet beetle larvae that feed on silk, wool, fur and feathers) and booklice. Booklice and silverfish can graze on mould, with higher numbers to be expected when there is intensely wet weather and high humidity.  

“Our booklice visitors appear to be more familiar within our collection spaces over the past few years,” Radford said.

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“Because mould is very appetising to booklice and silverfish, our collections and house teams continue to monitor areas that could be more vulnerable to mould outbreaks, allowing them to take a more targeted approach.”  

The five most prevalent insect pests in 2023:
  1. Silverfish (Lepisma saccharina)
  2. Webbing clothes moth (Tineola bisselliella)
  3. Booklice (Liposcelis bostrychophila)
  4. Woolly bear (carpet beetle larvae)
  5. Australian spider beetle (Ptinus tectus)

National Trust annual insect pest report 2023

Overall, insect counts were down by 11%, compared to the trust’s 2022 Integrated Pest Management data. This was likely aided by another year of turbulent weather, with record temperatures and rainfall, multiple named storms and rapid fluctuations. 

But the report also found that the traditional spring and summer breeding periods are continuing to merge into one, possibly driven by earlier springs and more protracted, mild autumns.  

Radford said: “In the past, we saw a more distinct spike in breeding cycles, but these are becoming blurred. Optimum breeding conditions are starting earlier and carrying on for a longer period of time to create one long reproductive season. 

Top Row: Larvae of a webbing clothes moth and (left) and silk webbing from a webbing clothes moth on the back of one of the 18th-century Tenier Tapestries, both at Blickling in Norfolk. Photo by Kenny Gray. Bottom Row: both images show damage from wood worm in a library book at Hughenden Manor in BuckinghamshireKenny Gray and Gill Sandford

“Nature is reflecting back the impact of these extremes. Without a doubt, the ongoing unpredictability and extremes in temperatures and moisture are feeding through into insect breeding cycles and patterns.” 

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An alarming 18% surge in clothes moths in 2021 at the trust’s historic houses was driven by lockdowns, but a heightened approach to integrated pest management along with recent hot and dry summers have helped bring this down.

Radford said the trust has put in place more training and resources to help property teams with integrated pest management, which is crucial to good collections care.

Understanding how weather and climate impacts breeding seasons is also helping house teams prepare for the peak times when nymphs and larvae begin to emerge and take action before they start causing problems for collections. 

Bees on the move

Meanwhile, a rare species of wild bee living in the roof a National Trust house in Gwynedd, North Wales, has been moved to a new home during conservation work.

The National Trust is undertaking on a project to re-roof Plas yn Rhiw for what is believed to be the first time in more than 200 years.

Five swarms with a total of about 50,000 Welsh black honeybees living in the roof of the building have been moved to nearby hives while the work is completed.

Thought to have died out in all but the most remote parts of northern Britain, the black honeybees were rediscovered in 2012 in some areas, including north Wales.

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