Trees in extreme southern Alabama are occasionally covered with what appears to be a mat-like cobweb in late August and early September. Homeowners describe their trees as being entirely covered with a giant silken web (see Photo 1).
This webbing is produced by small insects called bark lice and though the tree is apparently not harmed, the "ghostly" appearance may be somewhat disconcerting to the homeowner. The insects are probably common most years but are only noticed when populations are high and the amount of webbing becomes more apparent. When infestations are heavy the webbing may cover the tree including the main trunk, major and minor branches (see Photo 2) and even the above ground portion of roots (see Photo 3). However, although the webbing may cover virtually the entire bark surface, the foliage is not involved.
Bark lice apparently cause no damage to the trees and no control is recommended The webbing is quite thin and fragile and wears off as the season progresses. Heavy infestations seem to be associated with relatively long periods of high humidity, which may account for the fact that most reports in Alabama are from areas near the coast.
Bark lice, and their relatives, book lice, are small, soft-bodied insects that look somewhat like aphids (see Photo 4). These insects are not lice at all, they are not parasitic on anything. They are not pests of humans or animals and seem to be harmless, even to the trees they infest. They probably got the name because they are small and hard to see. Bark lice may have wings but wingless forms also occur. When winged, the wings are held roof-like over the back giving them the appearance of tiny cicadas. They are usually less than six millimeters in length. These insects belong to the order Psocoptera and are also known as "psocids". Bark lice feed on fungi, lichens and other debris found on the bark of trees. . The species that occurs in Alabama is probably Archipsocus nomas Gurney, which is found in the southern states from Florida to Texas.
Booklice, "first cousins" to bark lice, are wingless psocids, about one millimeter long. They are found in damp corners of buildings, musty storage cabinets and bookcases. They feed on fungi and other vegetable matter. The common name "booklice" is a result of the fact that they also feed on the paste in bindings of books, sometimes causing serious damage.
Contact your local County Extension Office for more information.
Coulson, R. N. and J. A. Witter. 1984. Forest Entomology: Ecology and Management. John Wiley and Sons. 669 pp. (See pages 67-68).
Craighead, F. C. 1950. Insect Enemies of Eastern Forests. USDA Miscellaneous Publication No. 657. (See page 81). 679 pp.
Day, E. 1996. Psocids. Virginia Cooperative Extension Service Entomology Department Factsheet.
Douce, G. Keith. Order Pscoptera: Psocids, Barklice and Booklice.
Lyon, W. F. Booklice. HYG-2080-93. Ohio State University Factsheet- Entomology. Ohio State University, Columbus, Ohio.
Photos 1-3 courtesy of Wayne Brewer
Photo 4 courtesy of the Brigham Young University slide collection, Kenneth J. Steins's Virtual Insectary and the Department of Entomology, Virginia Polytechnic Institute and State University