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Plaster Beetles/Psocids Infestation

May 28, 2021

EBS were asked to investigate plaster beetle infestation in new built apartments, which was causing the occupants some distress. The client required a positive identification of the insects, cause of infestation, associated health and safety implications and a method of control. 



Laboratory Identification

Insect samples were taken from the flats and examined in the EBS laboratory to identify the infestation.




These fast running stocky bodies and soft-bodied fragile insects were identified as Psocids and are commonly called Barklice or Booklice or Plaster Beetles because of their superficial resemblance to certain species of lice.  EBS previously found these insects on mouldy books, papers in damp buildings, basements and under loose, damp bark. 

They are either pale grey or pale brown in colour and may or may not have wings. They are common but harmless unpleasant nuisance pests.  Many live on bark and leaf surfaces feeding on algae, fungi or lichens.  Others are found in leaf litter, or in caves.  A small number have extended their range to include buildings and building materials such as thatch, stored food stocks and museum exhibits.


EBS Investigations

Varying levels of active infestation were noted in the flats during our investigations.

The majority of the infestation was found around the window trickle vents; however, insects were also seen in other locations including on walls, skirtings, in kitchen cupboards, bathrooms and extract fans. The infestation was prominent in both the ground floor and upper floor flats.



We were informed that a pest control company had fumigated or sprayed the flats, however the owners experienced re-infestation within three to four weeks of the treatment.  Varying levels of active Psocids infestation was noted in the flats during our site visit following the treatments. 



As the insects feed on mould, EBS carried out moisture meter and humidity tests to the fabric of the building to try and find any damp areas which could provide the conditions for mould growth which the insects would feed on.

No dampness could be found in the areas tested.



Borescope inspection 

Investigation of the dry linings and cavity wall voids was undertaken using a borescope in 8 selected apartments.  

Borescope inspection revealed no visible signs of insect infestation in the voids behind the plasterboard dry linings or in the wall cavities and the insulation was noted to be free of insect infestation.



Environmental Conditions

The Relative humidity in the voids behind the plasterboard dry linings was tested and was below 65% in all areas inspected indicating that the insulation was dry.



Environmental Control 

Psocids infestation don't spread diseases, bite, damage building fabric or contents, however, their sheer presence when found in large numbers in premises can be enough to cause anguish and distress to the occupants. 

Environmental control is preferable to chemical spraying treatments and EBS strongly believe that environmental control of infestations and preventative maintenance are preferable to conventional chemical treatments.  Spraying with chemicals will deal with the symptoms of the problem but will not deal with the causes of the infestation. 

The environmentally sustainable approach and the ongoing monitoring of the environmental conditions in buildings ensures the long-term health of building materials and the wellbeing of the occupants.  This approach avoids spraying harmful chemicals in the home.  

Psocids live and prosper in damp conditions and feed on mould infestation in buildings. Therefore, by dealing with the cause of the moisture and resulting mould growth, will be fundamental to their control.

Heating treatment offered by some companies, whereby the building is heated to 45°C should kill off Psocids in the building, however this does not address the underlying cause of the problem and there remains a risk of re-infestation.


For the prevention and control of Psocids infestation in the housing blocks, various remedial works were required.

Firstly, measures are required to fully investigate the environmental conditions.  The extent of damp and moisture mapping needs to be carried out to determine the residual moisture.

Measures are required to fully investigate the extent of environmental conditions predisposing to mould infestation, mould growth and the proliferation in cavities and voids.

The next stage is to carry out building works to deal with the causes of damp.  To execute remedial works to encourage drying of the building. The establishment of long-term environmental controls. 

It is important to encourage natural or accelerated drying of the wet fabric and to enable natural ventilation. 




EBS concluded that the infestation was due to residual mould growth in structural voids.  The building was open to the elements for a period during the build and the insulation became damp as a result.  The mould growth thrived in these conditions which resulted in the Psocid infestation.  Once completed the buildings gradually dried out particularly when occupied.  This prevented further mould growth and reports by the occupants that the numbers of insects are gradually reducing confirms this.  There will be some residual dead mould which the insects can survive on but we are confident the insects will disappear gradually.  An ongoing monitoring program will confirm this.