Tiny pests | PPC93 December 2018
When people think of house pests, it’s usually mice or cockroaches. We often overlook the tiny insects which may be living in British homes and eating your client’s clothes, furniture, books and even the house itself. Consultant entomologist, David Pinniger, shares with us some of the small but mighty pests you should keep an eye out for.
Man has been fighting tiny insect pests since Roman times when there are accounts of woollen clothes and feathers in centurion’s helmets being eaten. Tudor monarchs employed servants to beat the moths out of their carpets, and people used cedar wood chests to try and stop pest attack. Victorian times saw the introduction into the UK of many new species, including webbing clothes moths, with the rise in trade around the world. This increase in species accelerated in the late 20th century with new carpet beetles and woodborers and even more so in the last 20 years, which may be due to climate change.
Materials which are vulnerable to attack by insect pests include:
Wool: Clothes, carpets and upholstery
Fur: Clothes and taxidermy
Feather: Clothes and taxidermy
Silk: Clothes and wall coverings
Dried plant: Material baskets, dried plants and dried food
Paper: Books, wallpaper and photographs
Wood: Furniture, picture frames and structural timber.
Clothes moths and house moths
The moths which live in houses and attack and damage clothes and carpets are all small and relatively inconspicuous compared to the larger moths we may see attracted to lights in the evening. It is essential to be able to identify which species your client has, as they have different habits and food preferences. Adult moths can fly into buildings through windows or open doors, and some moths can also live in birds’ nests.
Dead animals, such as birds and mice, may also provide a source of food and support a moth infestation. The adult moths do not feed and therefore cause no damage; it is the grub-like larvae which hatch from the eggs which feed and damage our clothes and other items. One generation takes a year typically to complete the life cycle but, with webbing clothes moths, development can be more rapid if they are warm and undisturbed.
The pelleted excreta, or frass, produced by the larvae of moths is frequently mistaken for moth eggs. However, frass pellets are hard and opaque whereas moth eggs are very small and translucent and vulnerable to physical damage.
Contrary to popular opinion, clothes moth eggs will not remain dormant in textiles and then hatch many months later. Damage is more concentrated in dark, undisturbed areas, for example: wool carpet under heavy furniture, crevices and creases, behind lapels, in pockets or where carpets or textiles are folded. Clean cotton materials are generally not attacked.
TOP TIP
Adult moths are easy to kill with pyrethroid sprays, but larvae hidden in textiles are very difficult to control with insecticides. Clothes can be bagged and frozen for 2 weeks at -20°C to kill everything.
Biscuit beetles
The biscuit beetle (or drug-store beetle in the USA), Stegobium paniceum, is a worldwide pest, particularly in warmer countries. It belongs to the same family as the common furniture beetle or woodworm, Anobium punctatum, but unlike woodworm larvae, which eat wood, those of the biscuit beetle bore into hard, dried vegetable material including biscuits, nuts and dried cereals. Adults are very small reddish-brown beetles and when it is warm they are very active and will fly to lights. The larvae are white and curved and tunnel through hard materials.
The beetles emerge from exit holes which are very like furniture beetle holes and can bore through hard materials, including foil and plastic food containers to get out.
Biscuit beetles have an amazing ability to survive and breed on drugs and spices, some of which are extremely toxic to other animals. Infestations have been recorded from a wide variety of food including cereals, biscuits, dried bread, pasta, chocolate, dog food, stock cubes, curry powder, cumin seed and cannabis. A large number of biscuit beetles can be produced from a relatively small food source.
For example, hundreds of beetles were found in one building where they had been breeding in old mouse baits with wheat grains in trays. Biscuit beetle problems can be avoided by regular checking of dried food, storage in insect-proof containers and good stock rotation.
TOP TIP
You need a magnifier to make sure you can tell the difference between biscuit beetles and furniture beetles (see case study below).
Case study: A night at the museum
Some years ago, a museum in northern England found small beetles stuck on their pest traps which were identified by the museum’s pest contractor as furniture beetles.
The museum gallery had extensive exposed roof beams and so the contractor recommended spraying the wood as a precaution. The museum gallery was closed to the public for some days while the contractor sheeted over the display cases and sprayed all the beams with a residual insecticide.
After the treatment, I was given the traps to look at and found that all of the beetles were biscuit beetles with not a single furniture beetle to be seen. The beetles were not infesting the museum objects and so we then searched for a high starch food source nearby. One of the museum staff then mentioned there was a shallow attic above the gallery ceiling.
When we finally managed to gain access, it was full of bird nests and crusts of bread and other food dropped by the birds. This huge pile of infested debris was then removed by another contractor and the cleaned attic area sprayed with a residual insecticide. Result, no more biscuit beetles in the museum gallery below.
Key lessons
Identify the pest. If you get it wrong, it can result in extensive time-consuming and costly treatments which are totally ineffective and unnecessary. The first company lost the museum contract.
Silverfish and booklice
Many insects live in damp outdoor environments and if you disturb leaf litter or compost and look under stones or bark you will often see small creatures scurrying away. A few, such as silverfish, fungus beetles and booklice, are also able to survive indoors with humans, but only if the conditions give them enough moisture. This means that when you find them in your house it may be a warning that you have damp issues.
Silverfish are general scavengers and feed on starch, animal glue, surface organic material and microscopic moulds on paper. The most common species, Lepisma saccharina, will damage wallpaper, books, labels and photographs. Damage is caused by the insect scraping the surface causing eroded areas of thinned and weakened paper which eventually will break through to make holes. They are useful indicators of damp problems, and if found in numbers in an apparently dry room, it is likely that there are high humidity micro-environments nearby. For example, they are frequently found in kitchens and bathrooms and live happily in the damper areas behind skirting boards, under vinyl and lino floor coverings and underneath sealed-in baths.
If you find very large silverfish in London and Southern England it may be the grey silverfish Ctenolepisma longicaudata which is new to the UK. If you are not sure, get the identity checked by an expert.
The common booklouse Liposcelis bostrychophila is often found in small numbers in heated buildings. The adults are wingless and very small, less than 1mm. They feed on organic material and microscopic moulds on a range of substrates including flour, paper and cardboard. Although direct damage may not be so serious as caused by silverfish, large numbers of booklice will graze the surface of books and papers. To make things worse, squashed booklouse bodies will stain paper and may encourage moulds.
There have been a number of problems with booklice appearing in very large numbers in new or recently refurbished houses. The source has been traced to straw board used in walls and partitions.
The straw used in the board may contain enough residual fungal growth to feed booklice and allow them to breed rapidly and then emerge from gaps around doors and light fittings. Although they will eventually die out, this may take some years and treatment is very difficult.
Pyrethroid sprays will knock down adults if the problem is severe, but you also need to treat cavities and dead spaces with a desiccant dust.
Woodborers
The main pests of wood in houses are the furniture beetle or woodworm Anobium punctatum. Adult insects do not eat wood and apart from the round exit holes, cause little damage, but the larvae live in tunnels in the wood and cause damage which may range from a few holes in a picture frame to the complete destruction of floorboards or roof beams.
Furniture beetle infestations will survive in cool, damp conditions, but do not thrive in dry conditions with humidity below 55%. This means that objects and structural wood in well-ventilated centrally-heated buildings are very unlikely to support woodworm infestation. Outbreaks of woodworm activity are usually confined to outbuildings or areas which are damp due to leaks, condensation or poor air circulation.
It is very difficult to assess activity in autumn and winter. Fresh holes and frass will usually appear in spring and early summer.
The deathwatch beetle Xestobium rufovillosum is one of the most well-known and feared pests of timber. However, it is unlikely to cause problems in modern houses as it will only live in the old oak timbers found in historic buildings. Deathwatch beetle larvae will only develop in timber which has been damp and previously attacked by fungus, and an active infestation is often a sign that there are serious problems with water ingress.
People often panic when they find holes in furniture and structural timber because they don’t realise that the infestation may be long dead. It is therefore essential to distinguish between wood with active infestation of eggs and larvae, and wood which just has exit holes but no longer contains anything which is alive.
Paste tissue paper over areas which you think may be active and then check for fresh holes in spring. Very serious deathwatch beetle infestations may need a structural survey to establish if remedial work is necessary.
In summary: what can you do?
- Identify the species to find out if it is a pest and what is causing the problem
- Be aware of new species recently found, such as Australian carpet beetle and grey silverfish
- Find out if an infestation is active and where the insects are living by inspection or using insect traps
- Make sure the cleaning and housekeeping is targeting where the insects are living
- Isolate any infested objects and kill insects in clothing using bagging and freezing
- Only use insecticides if you are sure that the treatment will target the pest.
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David Pinniger has written the book (literally) on pests in houses. David and Dee Lauder’s ‘Pests in Houses Great and Small’ is a concise guide to some of the pest species that commonly infest historic houses, and solutions for dealing with them. It’s packed with identification tips and strategies for the removal of the pest and treatment options.
The book is priced at £14.99 and is available from Amazon and good bookshops including:
Source: PPC93