Web on tree limbs                Indian River County Extension Service
                                     1028 20th Pl, Suite D
                                     Vero Beach, FL 32960


FOR RELEASE: October 20, 2002
Daniel F. Culbert,  County Extension Director

                                                         BARK LICE MAKE SPOOKY WEBS

Halloween is a favorite holiday for kids of all ages - the chance to scare and be scared with spooky costumes and decorations can be  fun.  At this time of year, Mother Nature may join in the excitement of Halloween decorations by covering tree bark with a  mysterious webbing.  This spooky silken covering is produced by insects called Bark Lice, which may cause unnecessary concern among property owners. Information for today's column comes from University of Florida's Entomologists Don Hall and Jerry Butler and former Florida Division of Forestry Entomologist C. W. Chellman.

Bark Lice are more properly called 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, and have been reported locally on citrus trees.  Large numbers of adults and nymphs are occasionally observed on tree trunks often living underneath the fine silken webbing they construct.  These insects do not attack the tree, but feed on lichens, fungi, and dead animal and plant matter.

Peer carefully under the thin webbing that is found on tree bark, and look for the 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.

Usually, the first noticeable sign of the presence 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.

The 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 animal and plant matter, lichens and fungi.  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 away in a group - they  are commonly called tree cattle because of this herding habit.  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 to South Carolina.  They are distant relatives of the booklice, which are household pests that can consume wood and paper products.  These outside Bark lice 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 greatest populations are found in the fall before the onset of cooler weather.

Managing your Tree Cattle
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 removing these insects, a Pest Control Operator may be contracted to apply a legal insecticide.

A recent Featured Creatures article on Psocids is available at our office or on the Internet through our county Extension website at http://indian.ifas.ufl.edu.  If you need additional information on tree cattle, call or stop by our office.  For other questions about Florida Yards, our office holds Master Gardener Clinic hours at the Extension office (1028 20th Place, Suite D, Vero Beach) during office hours, Wednesday morning at the North County Library in Sebastian, and the first Saturday of the month at the Environmental Learning Center. Our phone number is 770-5030, and you can email us at indian@ifas.ufl.edu.



Butler, Jerry F. &  Hall, Donald W.  Webbing Barklouse  (Featured Creatures,  EENY-275 ) Gainesville: Florida Cooperative Extension Service , October 2002.

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.

 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 .

Goode, Don.  Disease wreaks havoc on freeze-damaged shrubs, trees. Lake City: Lake City Reporter, June 26, 2002.

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.

Sweat, Mike.    Psocids (Tree Cattle) Causing Tree Webbing Baker County Extension Service - Current Agricultural Topics

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