Bark Lice: A Guide To Understanding This Insect


The presence of webbing and a colony of small insects may indicate a bark lice infestation. 

“Bark lice” is the common name for Psocoptera. 

colony of bark licecolony of bark lice

They are small brown insects feeding on the debris found on the bark of trees and shrubs.

Bark lice frequently appear on trees and shrubs with smooth bark, such as Crepe myrtle and oaks. 

They may also occasionally infest hardwood plants. 

Keep reading to learn how to deal with an infestation.

What Are Bark Lice?

Bark lice are insects often found on the bark of trees. 

While they are called bark lice, they are not lice. 

Unlike lice, Psocoptera is not parasitic or pests.

Psocoptera is one of the oldest species of insects, first appearing over 250 million years ago. 

Psocids are scavenging insects with long antennae and small chewing mandibles.

The critters only measure about 1 to 10 millimeters in length and resemble aphids. 

However, unlike aphids pests, they do not pose a threat to plants.

The telltale sign of bark lice is the development of webbing on the bark of the tree and a large cluster of shiny little insects. 

If the tree contains yellow or distorted leaves or black sticky substances, the tree most likely contains aphids instead of bark lice.

Psocoptera colonies often include hundreds of “lice” with a mixture of adults and nymphs. 

When the nymphs mature, they develop wings. 

The wings are typically only used for dispersal when the colony is disturbed.

There are many species of bark lice found throughout the world. 

No matter the species, they have soft bodies and shield themselves with a thin layer of silk. 

The insects weave the silk themselves, and it eventually covers large portions of the bark of trees.

These psocids eat a wide variety of organic materials, including fungi and mold. 

They prefer moist environments and search for decaying matter.

Along with climbing on trees, Psocoptera often appears in moldy old books, leading to the common name “book lice.”

A colony of bark lice or book lice often indicates the presence of mold or fungal growth. 

In a way, these critters help homeowners identify potential issues in their gardens or landscapes.

What Damage Do Bark Lice Cause?

  • Bark lice do not cause damage. In fact, they are considered beneficial to the health of trees. 
  • As bark lice spin their webs and slowly spread across the tree trunk, they eat a wide variety of substances which may pose health risks to trees. 
  • Bark lice help clean up algae, fungi, mold, and dead plant tissue.
  • Outdoor bark lice are not an issue. 
  • Unfortunately, they may cause problems indoors. 
  • The insects may eventually work their way to the kitchen while searching for spoiled food.
  • If the insects gain access to any food containers, they may contaminate the food. 
  • This is the one potential risk with bark lice, and it only occurs indoors.
  • Indoor bark lice are incredibly rare. 
  • The most common way for these insects to appear indoors is on live Christmas trees. 
  • If the tree already contains a bark lice colony, the colony may stay on the tree as it is brought home and carried inside.
  • Once inside, the warmer air forces the insects to search for food. 
  • Without access to spoiled food or organic material on plants, the insects quickly die out.
  • The only potential issue with bark lice on plants is the appearance of their webbing. 
  • However, at the end of the growing season, the bark lice consume their own webbing. 
  • They clean the tree throughout the warmer months and then clean up after themselves.
  • Along with posing no health dangers to the tree, bark lice pose no health risks to humans and pets. 
  • These insects are not known carriers of any diseases and do not bite.

How Do You Control Bark Lice?

As bark lice are not pests, the typical recommendation is to avoid disturbing a bark lice colony. 

Leaving the insects to complete their job benefits the tree.

Psocoptera do not bore into the bark or damage the leaves. 

They simply eat the organic materials growing on the bark of the tree.

While bark lice are not a threat, some people dislike the appearance of Psocoptera colonies on their trees.

To remove black lice, simply spray the tree with water. 

Almost any activity sends the insects flying away. 

The water also easily removes the webbing. 

There is no need to use insecticidal soap or other commercial pest treatments.

When disturbed, black lice tend to leave in groups, as with a herd of cattle. 

This behavior has led to the common names “bark cattle” and “tree cattle.”

Within a few moments, the insects may reappear in their original spot. 

In some cases, it may take several strong sprays of water to remove the colony from a tree fully.

The bottom line is instead of treating a bark lice infestation, the insects should be left to complete their cleanup job.

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