Glistening web on tree bark is harmless

Many people notice fine silken webbing on the trunks and branches of their trees and assume that this is a problem. But the insects that cause this webbing are not harmful to trees. They could even be considered beneficial.

The tiny insects that make the webbing are called psocids (pronounced so-cids). They are sometimes called bark lice. They feed on lichen, moss, algae, fungi, spores, pollen and possibly the remains of other insects found on the tree’s bark. As a result they sometimes are referred to as bark cleaners.

Because the webbing appears suddenly on a tree’s trunk and/or limbs, many homeowners wonder how it got there, where it came from and if it will damage their tree. The cause for the webbing can be seen if the webbing is pulled from the tree. Underneath you’ll see brownish-black insects approximately ¼ inch in length with some white markings. When webbing is removed, the insects usually move away in a group and are commonly called tree cattle because of this herding habit.

Some people will see the webbing as it glistens in the sun, walk to the tree and visually inspect it from top to bottom – much closer than they’ve ever inspected the tree. They might notice a dead branch or other imperfections in the tree and then wrongly blame the tree cattle. I’ve talked to homeowners that sprayed their trees with insecticides or that hired pest control businesses to treat trees as a result of finding the webbing. One person needlessly cut down a tree after finding the webbing assuming he was dealing with a pest that was going to move through his neighborhood and injure/kill trees.

The immature insects (nymphs) remain together under their silk like webbing, which they produce as a protection from weather and predators. Adult psocids have wings that are held roof-like over their body. Nymphs are wingless.

These bark cleaners are harmless so control measures are not recommended. If the webbing is considered unsightly, a heavy stream of water from a garden hose can be used to wash insects and webbing off infested trees.

If nothing is done, the webbing usually goes away in several weeks. Psocids can be found on many rough-barked hardwood trees and palms. Most people seem to find them on oaks more often than other tree species, though.

Bark psocids are more active during the warmer, wet weather of spring and summer.

For additional information on Florida insects, contact the University of Florida IFAS Extension Office in your County or visit the Featured Creatures website, at http://entnemdept.ufl.edu/creatures.

Larry Williams is the Extension horticulture agent with the Okaloosa County Cooperative Extension Service, University of Florida. Contact Larry at 689-5850 or email lwilliams@co.okaloosa.fl.us.