Storing flour

If your food cupboards become infested with tiny grey or brown insects, these are called psocids (pronounced so-sids) They are often found on the packaging of dry goods such as flour, powdered milk, sugar or semolina. 

What are psocids?

Psocids- or booklice – which are often between 1 and 2mm long may be found in dry foods. They are not caused by poor hygiene, and can be found in the cleanest of cupboards. They prefer to live in dark, warm, humid places – such as the folds of packaging in food cupboards, and dislike light or disturbance.  They feed on a wide variety of food products – such as flour – and also the microscopic moulds that develop in humid conditions. They may live for about 6 months during which time the female may lay up to 100 eggs.  Several independent studies have shown that the psocid species which causes the majority of problems in homes, is rarely found where food is produced

Conditions

Psocids prefer areas with high humidity but can tolerate dry conditions for some days. The kitchen environment is likely to provide the conditions they need and fitted cupboards provide the darkness that attracts them. Some food products, including flour, naturally contain moisture.  In warm conditions psocids can rapidly increase in number.  This is most likely to occur during the summer months when temperatures are higher, leading to their discovery in the autumn.

How to prevent psocids

It is often wrongly assumed that the flour is the source of the infestation. This isn’t the case. It’s the fact that flour provides the perfect condition for them to be. 

• Packets of food that have been opened should be used up quickly and not pushed out of sight to the back of the cupboard.
• Food storage areas should be well ventilated and cool.  (Liposcelis bostrychophila, the psocid that is overwhelmingly the most important psocid pest in the domestic situation, likes warm humid conditions. Cold and dry situations are unfavourable for its survival.)
• If storage in cool ventilated cupboards is not possible, make sure that your cupboards are always free from condensation and damp.  If you notice that condensation occurs in your kitchen, particularly during cooking or washing, open your windows.  If the problem is continual, it may be necessary to take additional precautions.  Advice on preventing condensation should be sought from the local Environmental Health Department.
• Any potential hiding places should be sealed with paint or mastic.  Many fitted kitchen cupboards are made from laminated chipboard and the surfaces, which are not on view, tend not to have a laminated finish.  These unfinished edges can provide crevices for the psocids to hide in and should be sealed with a coat of paint or varnish.
• Regular cleaning of cupboards is advisable, since crevices of cupboards harbouring dry food can also provide a food supply for psocids. Use of a vacuum cleaner is recommended, provided the contents are then immediately disposed of in an outside waste bin.  Do not use a very wet cloth since this may seal dry food into crevices, encourage humidity and the growth of mould in chipboard.