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University of Minnesota Extension

Psocids (barklice, booklice)

Quick facts

  • Psocids (pronounced SO-sids) 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.

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 color.
  • Psocids have either four wings or are wingless.
  • They have a large nose called a clypeus.


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 molds, fungi, grains, insect fragments, and other starchy material, including glue from bookbindings.
  • In homes, psocids typically are found in damp, warm, undisturbed places where mold 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 mold problems.

How to manage psocids

Ignore small numbers of psocids. You can choose to physically remove them, including with a vacuum.

If they are numerous, the most effective method to manage booklice is to reduce moisture. Psocids do not survive when humidity falls below 45% - 50%.  

To reduce humidity:

  • Use a dehumidifier or fan to air out rooms and keep the air moving.
  • Check rooflines for poor attic ventilation, trees overgrowing the roof, and leaf litter in the eaves. Correct any of these conditions.
  • If there is a crawlspace under a home, a pest management company can check to see if there is adequate ventilation and that the crawlspace is dry.
  • Store boxes, bags, books and papers off the floor to minimize exposure to dampness.

Using pesticides

Insecticides are normally not necessary. Insecticides are not effective if moisture is still a problem. The products that are typically available to residents are generally not effective against psocids.

Jeffrey Hahn and Stephen Kells, Extension entomologists

Reviewed in 2019

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