Psocids (Booklice) – From time to time people find that their food cupboards have become infested with tiny grey or brown insects. These are often found on the packaging of dry goods such as flour, milk powder, sugar or semolina. It is natural, but often incorrect, to assume that the products themselves are always at fault. Our aim is to explain what these insects are and how best to prevent them.

What are Psocids?

Psocids or booklice are common but harmless insects between 1 and 2 mm long, which survive in dry powdery foods. They prefer to live in dark, warm, humid places such as the folds in packaging in food cupboards, and dislike light or disturbance. They feed on a wide variety of dry food products such as flour and also the microscopic moulds that develop in humid conditions. They may live for over six months during which time the female may lay up to 100 eggs. Research has shown that the sort of psocids (there are several different species) which cause problems in homes are rarely found where food id produced.

What Causes Them?

They prefer areas with high humidity but can tolerate dry conditions for some days. The kitchen is likely to provide the conditions they need and fitted cupboards provide the darkness which attracts them. Some food products, including flour, naturally contain moisture. Moisture in the home can be caused by not having enough ventilation in the kitchen or bathroom. In warm conditions they 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.

Prevention and Cure

It is best to keep all dry foods in cool larders or cupboards with ventilation. If this 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 may be sought from the Private Sector Housing Team. If you discover any insects, do not use an insecticide because of the danger of contaminating your food. The best method of getting rid of them is to remove and dispose of all the affected food. Clean the cupboard by using a dry cloth and empty the contents into an external dustbin. Make sure the cupboard is completely dry before replacing any foods. This may be achieved by using a warm air blower like a hair dryer.