Psocids (also called booklice) are very common insects. The types of psocids that infest buildings are usually light-coloured and very small (about 1 - 2 mm long). They do not jump or fly.
Psocids feed on microscopic moulds. They can become very numerous in damp or humid, warm and undisturbed situations which encourage mould growth. They can often be found in great numbers in damp grain, musty books or around unhealthy houseplants. In kitchens, they can become numerous when steam from cooking or boiling kettles creates favourable mould growth in nearby cupboards. They do not do damage of any kind.
It is likely that most buildings have small numbers of psocids living in them. Finding an occasional psocid should not, therefore, be cause for alarm. When present in large numbers, however, they can be a nuisance and steps should be taken to control them.
Large populations of psocids are indicators of excessive moisture. Control of these insects is, therefore, achieved by controlling the humidity. This may involve finding and fixing leaks, improving air flow, installing dehumidifiers, using double-glazed windows, altering drainage patterns around buildings or changing cooking practices.
Short-term control can sometimes be achieved by disposing of heavily infested materials, thorough vacuuming and/or use of household disinfectants to kill the moulds on which the psocids feed.
Pesticide use is almost never worthwhile.