Psocids or Book-lice - Elite Pest Control Ltd

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Psocids or Book-lice

Quick facts

  • Psocids are common outdoor insects, although some species are occasionally found inside buildings.
  • They rarely cause damage and are mostly just a nuisance.
  • They do not harm people or pets.
  • The best way to manage psocids in homes is to reduce moisture.

Psocids or Book-lice

They have long, filamentous antennae and a  characteristic bulging clypeus (the area just above the mouth parts). They have chewing mouth parts and the wings of domestic species are usually absent. They range in size from 1/25 to 1/13 of an inch (1 to 2 mm) in length. Colouration is from almost colourless to grey or light brown.


Psocids feed upon microscopic moulds. Thus, any manufactured material of plant origin that would support the growth of these moulds is susceptible to their attack. They are found in nature on the bark of trees and shrubs, preferring damp, warm, undisturbed environments. They can commonly be found in books and book bindings, storage boxes, paper and goods 

Life Cycle:

Psocids undergo simple metamorphosis to develop to maturity. Eggs will hatch 21 days after being laid. This nymph will reach sexual maturity in 24 to 65 days. Females lay anywhere from 20 – 50 eggs depending on the time of year. Their total life span is from 24 to 110 days.

Facts, Identification & Control

Latin Name : Order Psocoptera


How to identify psocids

  • Psocids are soft-bodied insects.
  • They are less than 3/16 inches long with long, slender antennae.
  • They are generally white, gray or brown in colour.
  • Psocids have either four wings or are wingless.
  • They have a large nose called a clypeus.

There are more than 200 species of psocids (often pronounced “so-sheed” or “so-sid”). 

Most psocids are tiny insects. Depending on the species, the size ranges from 1 to 6 mm. The colour of psocids varies according to the species. Psocids that live outdoors often have wings. Psocids that invade homes usually have very small wings or no wings at all.

Psocids have chewing mouthparts, but they do not bite people or pets. When they invade kitchens, they can contaminate open packages of food.

Behaviour, Diet & Habits

Psocids are tiny insects that live in damp environments. They eat mould and mildew. Some people call them barklice or booklice. The name barklice probably comes from the fact that outdoors they gather under the bark of trees. The name booklice comes from the fact that they gather on mouldy books in damp homes. Experts think that the sizing and starch in the bindings of books supports mould growth in humid environments.

Psocids invade areas where there is dampness and mould, like basements and crawlspaces. They also infest areas where a plumbing leak causes mildew or mould to grow. Psocids have infested bath traps with leaking or sweating pipes. They have also infested air conditioning drain lines. They feed on mould in their damp environment.

Psocids often seem to appear suddenly. This may be because they are so small that people do not notice them when there are only a few around. Some people think psocids look like tiny termites.

Psocids cannot retain water in their bodies, so they are sensitive to changes in humidity. A key step in controlling psocids is reducing the humidity in their environment. When the humidity is low, the psocids will die. If the humidity stays low, they will not re-infest.


The females lay eggs in the spring and summer. The immature insects are called nymphs. They look like the adults but have no wings.The main sign of psocids is the sighting of the psocids themselves on surfaces or in products.


Make a careful inspection to find the moisture sources. If psocids are active in the kitchen, start the inspection under the sink. Empty the cabinet if necessary. Inspect every area that has plumbing. In the bathroom, there should be a trap door near the head of the bathtub for access to the pipes. Inspect tile walls carefully. If grout is missing, mildew can grow behind the tiles.

There can be other moisture sources besides the plumbing. Look at the gutters and downspouts. Make sure they are not blocked. Downspouts should drain away from the foundation.

Check the crawlspace vents. They should be open in warm weather. If there is moisture on basement walls, specialists at the home store can recommend ways to waterproof them. A dehumidifier can also help reduce moisture in a basement.

The local pest control professional can select techniques that are effective in the situation.


Most psocids live outdoors and have wings and are known as barklice. 

  • They are found on tree bark, leaves of trees and shrubs, and under stones.  
  • They can become obvious when they assemble in large numbers.
  • Barklice feed on fungi, lichen, pollen, decaying plants and other organic material.
  • They are harmless to plants and treatment is not needed.


Some psocids (usually Liposcelis spp.) are wingless and can be found inside buildings. They are called booklice because they are often found near books or paper.

  • Booklice are rarely damaging inside homes and are harmless to people or pets.
  • Booklice usually feed on moulds, fungi, grains, insect fragments, and other starchy material, including glue from bookbindings.
  • In homes, psocids typically are found in damp, warm, undisturbed places where mould and fungi are growing.
    • People commonly find them during summer.
    • They can cause problems if stored cardboard becomes wet.  
  • They can be a nuisance in large numbers.

In food

  • Psocids are sometimes pests in commercial food storage and food manufacturing facilities. 
  • Psocids in food indicate fungal or mould problems.