Okeechobee County Extension Service

458 Highway 98 North

Okeechobee, FL 34972

Phone: (863) 763-6469

E- mail: dfculbert@ifas.ufl.edu 

Feature Article - for release the week of July 27, 2003

Daniel F. Culbert - Extension Horticulture Agent

It’s that time of year when a mysterious webbing is noticed on branches and limbs of shade trees. Our office has had several calls and visitors who want to know what is causing this stuff, and what can they spray to get rid of it. The short answer is that these harmless insects called barklice are now rapidly increasing in number. A strong spray of plain old water will loosen their grip.

Barklice are more properly named Psocids (pronounced "SOSS-sids"). They are also called tree cattle because of their habit of living as a group on the bark of hardwoods, particularly oaks. They also sometimes noticed on citrus trees. Large numbers of adults and nymphs are occasionally seen on trees, living underneath a fine silken webbing. These insects do not harm the tree, but feed on lichens, fungi, and dead animal and plant matter.

Webbing on tree bark may be due to insects.  The webbing pictured here is NOT  a problem - it is due to Psocids. However, certain  caterpillars and mites can produce webbing that may indicate a pest problem.  Photo: Dan Culbert, UF/IFAS

Under the webbing live hundreds of Psocids, a.k.a. Bark Lice.  They feed on lichens and dead bark - and do not harm the tree. Photo: UF/IFAS Jim Castner

If you look carefully under the thin webbing that they secrete, you may see one-quarter inch long adult Psocids, which are brownish-black in color. Their wings will be brown with some white markings, and appear like a roof over their body. The younger nymphs will be smaller and look like the adults except that they are wingless. Eggs are small and are whitish in color.

The first noticeable sign of this insect is the fine silken webbing. The bark lice secrete this as a protective covering on the bark. This silken webbing has a silvery sheen and may cover parts of the tree trunk and large limbs. When the webbing is pulled off, it is not uncommon to see hundreds of these insects. This webbing is not found on the twigs or leaves, and looks different than webbing produced by destructive caterpillars.

Adult female Psocids lay their eggs in clusters or piles on leaves, branches, and the trunks of trees. Upon hatching, the nymphs begin to feed on dead insects and plant matter, plus the lichens and fungi which naturally occur on tree bark. They are usually gregarious, which means the adults and nymphs will remain together under the silken webbing. When the webbing is removed, they usually all move in a group, much like a herd of "tree-cattle. There are several generations a year in Florida.

Webbing barklice are found throughout Florida, and along the Gulf coast from Texas and along the Atlantic coast north through South Carolina. They are distant relatives of the booklice, which are household pests that can consume wood and paper products. These outside barklice are not a threat to either the inside environment or to Florida Yards.

Populations of these tree cattle rise and fall with the seasons. Cooler weather kills off many in the winter and as springtime temperatures rise, food sources increase and more webbing appears. The number of barklice increase rapidly in mid summer and the greatest populations are found in the fall before the onset of cooler weather.

No control measures are recommended for these insects. If the property owner objects to the webbing of these insects, a strong blast of water from a hose will dislodge them from the tree. But as scavengers, they perform a valuable function in consuming excess accumulations of lichens, dead bark, and other materials found on the outside of the tree. On trees that are regularly sprayed with insecticides for other pests, psocids will rarely be seen. If the homeowner does insist on killing these insects, a Pest Control Operator may be contracted to apply a legal insecticide.

The University of Florida can refer you to more information on barklice and other information about your Florida Yard. Please contact our office if you would like additional assistance, or call or stop by our office at 458 Hwy 98 North in Okeechobee. Our phone number is (863) 763-6469, and you can email us at okeechobee@ifas.ufl.edu .

The Florida Cooperative Extension Service - Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational information, and other services to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin. Larry A.  Arrington, Dean.  Last update: 08/10/2007 .  This page is maintained by Dan Culbert.

Butler, Jerry F. & Hall, Donald W. Webbing Barklouse (Featured Creatures, EENY-275 ). Gainesville: Florida Cooperative Extension Service, October 2002. http://creatures.ifas.ufl.edu/trees/barklouse.htm

Chellman, C. W.    Psocids or Tree Cattle.  FDACS  Division of Forestry Forest & Shade Tree Leaflet #34.  June 1969 (rev. Aug. 1973).

Day, Eric. Psocids. Blacksburg, VA: Virginia Cooperative Extension Service.
http://www.ext.vt.edu/departments/entomology/factsheets/psocids.html

Don't fear ghost-like look on tree.  Jacksonville: Florida Times Union. May 17, 1997.
http://www.jacksonville.com/tu-online/stories/051797/0517delv.html .

Hunsberger, A et.al.  Bark Psocids.  Homestead: UF/IFAS, August 2006.  http://mannion.ifas.ufl.edu/pdfs/Bark%20Psocid.pub%20(Read-Only).pdf

Lippi, Chuck.  Bunnell: Flagler County Extension Service - Flagler Horticulture column, July 4, 2001.
http://www.flaglercounty.org/extension/county2n.htm .

Mullins, Dan.  Fine Silken Webbing on Trees No Cause for Alarm. Tallahassee: Leon County Extension Service July 11, 2002. http://leon.ifas.ufl.edu/fine_silken_webbing_on_trees_no.htm

Rudisill, Ken.   Tree cattle: Grazing on trees, shrubs.   Panama City: News Herald, August 21, 2000.
http://www.newsherald.com/articles/2000/08/21/gs082100a.htm

Sweat, Mike.    Psocids (Tree Cattle) Causing Tree Webbing Baker County Extension Service - Current Agricultural Topics
http://baker.ifas.ufl.edu/ag_topics.htm

Williams, Larry. Tree cattle are insects, but they are definitely not pests.  Destin, FL: Northwest Florida Daily News July 8, 1999. http://www.nwfdailynews.com/archive/gardening/990708newsgard.html