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

Hilary Jarvis, Assistant National Conservator Hilary Jarvis Assistant National Conservator

What can you do if you discover that something has been feasting on your favourite woolly jumper or carpet? Hilary Jarvis, one of the National Trust’s Assistant National Conservators, shares tips and thoughts and looks back on the most common pests found in 2021 at National Trust houses during a year that saw us emerge from lockdown and throw open our doors once again.

Insects are a critical part of our ecosystem, making up more than 80 per cent of the animal kingdom. They are also a fact of life in our historic houses. Many species, including spiders and ladybirds, are perfectly harmless. Others, like clothes moths and carpet beetles, are less welcome because of the damage they can wreak to our collections.

Small but destructive

Only a tiny proportion of the UK’s insect species damage our collections and interiors. However, the few that do, can become serious pests and cause irreversible damage to our objects in a short period of time.

Among the worst offenders are silverfish (Lepisma saccarina), webbing clothes moth (Tinneola bisselliella) and varied carpet beetle (Anthrenus verbasci). These pests, or more usually their larvae, will happily graze on a host of objects including books, wallpaper, textiles and taxidermy.

Five most common insect pests in 2021

Last year our staff identified and logged 56,742 insects at the places we care for.

The five most common insect pests found in 2021 remain the same as those recorded in 2020, although interestingly there has been movement at the top with the webbing clothes moth knocking silverfish out of the number-one spot.

Here's the fascinating, yet troublesome pests that topped the leaderboard.

  • Webbing clothes moth (Tineola bisselliella) rose 18 per cent, leaping to the number one spot.
  • Silverfish (Lepisma saccharina) slumped 31 per cent to the number two slot last year, continuing their decline from a 2019 peak, possibly due to drier conditions overall across the year.
  • Australian spider beetle (Ptinus tectus) numbers are at last showing signs of retreat, although they remain high at Tredegar in Wales and are growing at three sites in Northern Ireland. They remain a decidedly 'north of the Midlands' phenomenon, with regional weather trends likely to be the determining factor as we see warmer, wetter winters. They are also very difficult to evict, once embedded.
  • Common booklouse (Liposcelis bostrychophila) came next in 4th place, outdoing Woolly bear, after a sharp increase in 2019 and a steady climb in 2020.
  • Woolly bear (a generic term for various carpet beetle larvae), came in at number 5 on the list for 2021.

Your visits help to protect precious collections 

Insect pests such as moths and silverfish thrived during lockdowns. With less disturbance and relative darkness providing the perfect conditions for pest larvae and adults, their numbers increased by 11 per cent during this time. However, their efforts were slowed in 2021.

With the reopening of houses come May, visitors unknowingly played an important role in keeping pests at bay, helping drive a 6 per cent downturn in moths, silverfish and other insects that can cause damage to historic collections.  Despite this, warmer, wetter winters are leading to an increase in pest breeding cycles and helping some pests increase their range by moving north.

Identifying the culprits
Adult webbing clothes moth

Webbing clothes moth 

Webbing clothes moths give off pheromones to attract mates over long distances. At Blickling Hall in Norfolk, we’ve started a pioneering trial using pheromone ‘tabs’ and tiny parasitoid wasps to help control the clothes moths, which can cause serious damage to our collections. This will help us safeguard treasured items such as the ‘Peter the Great’ tapestry, which was gifted by Catherine the Great to Blickling’s then-owner in the 1760s.

Blicking's moth control trial
Monitoring the pest population

Silverfish

Silverfish are shiny, slithering insects that thrive in damp conditions and are often found in kitchens, bathrooms and basements. Here, a member of staff on the lookout for silverfish inspects a pest trap at Baddesley Clinton, Warwickshire.

An illustration of a carpet beetle

Carpet beetle

Carpet beetles won't actually damage your textiles, but their larvae will. Numbers can skyrocket if the adults are left undisturbed to lay eggs in natural fibre items. Regular vacuuming is the best preventive measure, but an insecticide may be needed to deal with carpet beetle larvae, also known as 'woolly bears'.

Tell-tale signs of insect pest damage

Silverfish damage to wallpaper

Silverfish grazing

Silverfish feast on paper, fabric and glue and are known to prefer particular pigments or dyes, which may explain the concentrated areas of damage to this section of wallpaper at Chastleton in Oxfordshire.

Webbing clothes moth damage to felt curtains

Webbing clothes moth damage

Webbing clothes moths can cause significant damage to textiles and natural history collections. The larvae feed on keratinous material, leaving ragged patches or holes, as in this felt curtain at Hughenden Manor in Buckinghamshire. Here you can see the tell-tale silk webs left by the adult of this particular moth species.

Carpet beetle damage to the ermine of the Whistler room curtains

Carpet beetle nibbling

Carpet beetles won't just eat carpets - they'll happily eat your upholstery, curtains and clothing. A series of holes can mean you are dealing with a large infestation. Here, carpet beetle damage can be seen on the mock-ermine wool linings to the green velvet curtains that hang in the Whistler room at Mottisfont, Hampshire.

Prevention is better than cure

In order to deter unwanted insect guests in our historic houses, we adopt a preventive approach, combining the best traditional housekeeping knowledge with modern conservation science. If you find yourself sharing your home with uninvited creepy crawlies, here's a list of things you can do:

  • Seal gaps in windows and doors. Insects are getting in from somewhere, so stop up the obvious places
  • Call in the sweep! When birds create nests in your chimney they are also creating homes for insects too
  • Be mindful of shrubs and plants growing right by your windows. Adult beetles eat plant material but will come indoors to lay their eggs on your wool, silk, fur or feathered objects
  • Consider turning down your thermostat a notch: bugs and beasties generally prefer warm, cosy environments, so if you are struggling with a stubborn resident, try keeping your home (or maybe a certain room) a few degrees cooler
  • Most insects struggle if the air is too dry, so if you do have damp rooms or problems with leaks, you may find yourself quite popular
  • Leave your wardrobe doors open from time to time to allow the air to circulate and to let in sunlight
  • And make sure your favourite garments have been washed or dry cleaned before you pack them away, as moths rarely eat clean silk or wool.

Above all, our number one recommendation is good housekeeping, which really is the answer in most cases. 

Ventilation is critical for wool, silk and fur, such as these period clothes in the Dressing Room at Greenway, Devon
Period clothes and luggage in the Dressing Room at Greenway, Devon, which was the holiday home of the crime writer Agatha Christie.
Ventilation is critical for wool, silk and fur, such as these period clothes in the Dressing Room at Greenway, Devon
We make sure our garments are clean before going into store, as with this 19th-century silk wedding dress from the collection at Charlecote Park, Warwickshire
Detail of the white silk wedding dress worn by Mary Elizabeth Williams when she married George Hammond Lucy at Charlecote Park, Warwickshire
We make sure our garments are clean before going into store, as with this 19th-century silk wedding dress from the collection at Charlecote Park, Warwickshire

Spring clean, anyone?

Historically, most of our houses would have been closed at some point in the year, usually in the winter. House staff would have used this as an opportunity to strip rooms down and give them a thorough clean. They’d also be on the lookout for insect pests or damage.

This is still the case in some of our houses today, so on top of your general housekeeping, consider giving each space a really good spring clean every year.

Use a soft rubber pet brush and your vacuum crevice tool for reaching tight, carpeted corners and skirting boards. Try to vacuum busy hallways and stairways regularly to remove the dirt, dust and debris that can also act as insect food. Plump up cushions and try to vacuum underneath furniture from time to time.

Insects like to be safe and undisturbed, so think like an insect and try and see your living space with their buggy eyes!

 

Remedies and eradication

If you do find a jumper with a hole in, pop it in a plastic bag and leave it in the freezer for about 14 days. This will kill any remaining eggs that you might not be able to see and which can survive the lower-temperature washing machine cycles we favour today.

Nibbled carpets are not easy to repair. Have a good go with the vacuum cleaner and consider tracing over the chewed area with a soft pencil on a piece of paper. This will give you a record of how big it is, and you will know for sure if another insect friend has found the same spot.

If circumstances like this we might considering using an insecticide, incidentally, to try and limit the risk of further damage. We a use colourless, biodegradable chemical that is harmless to pets or humans. The residue can kill returning insect pests before they start nibbling. You can find a range of products in most hardware stores these days.

" Our number one recommendation is good housekeeping"
- Hilary Jarvis

We’ll never be rid of insects and generally find we can co-exist perfectly happily. Our primary role is to ensure our special places are there to be enjoyed for everyone, forever, so we need to be ready if we find too many critters getting overly comfortable. Hopefully you can now be a bit more insect-pest ready too!