What Is The Difference Between Psocids, Booklice And Barklice, And Which Of These Insect Groups Are Known Pests That Damage Property?

The insects commonly known as psocids belong to the order Psocoptera, which is made up of numerous species that can be found throughout the world. These insects thrive in high moisture conditions including damp grass patches, dead vegetation at the base of trees and shrubs, in damp wood, beneath lichens and moss, and behind tree bark where they feed on mold, mildew, pollen, decaying plant matter, and other forms of organic waste. Most psocid species possess wings and dwell exclusively outdoors where they often become numerous on residential and commercial properties, especially properties where trees and organic waste is abundant.

Outdoor-dwelling psocids that infest trees in large numbers are commonly referred to as “barklice,” and they are often mistaken for pests due to their habit of using their silk to cover trees in white webbing. Barklice construct a silk sheath over the trees they inhabit in order to protect their soft bodies from water loss. While homeowners may consider these webs unsightly, barklice themselves are not harmful to trees; instead, barklice are beneficial because they eat harmful microorganisms that grow on trees including algae, fungi, lichen, dead bark, and various forms of organic debris. While outdoor psocids are beneficial on properties, their indoor counterparts are another story.

Psocid species that are known to dwell indoors are commonly referred to as “booklice” due to their habit of feeding on paper and adhesive in the binding of books. Indoor booklice also feed on molds, fungi, grains, cardboard, insect fragments, and virtually any starchy material. Most booklouse infestations see numerous specimens invade homes where they gravitate toward humid and warm areas where their mold food source can be found growing. While a large number of booklice pose a tremendous nuisance, their indoor presence often leads to the discovery of potentially harmful sources of mold hidden within homes.

Unlike barklice, booklice are wingless indoor pests that establish nuisance, and sometimes, economically costly infestations. Barklice and booklice are so named because of their louse-like appearance, and not because they suck human blood. A small number of indoor booklice can be removed with a vacuum, and larger infestations can usually be controlled by correcting indoor moisture problems that can result from pipe condensation, poorly ventilated crawl spaces, clogged gutters, excess vegetation surrounding foundations, and rainwater and plumbing leaks. Psocids cannot survive conditions where relative humidity is below 50 to 45 percent.

Have you ever encountered booklice in your home?