Prepared by Powell Smith, Extension Associate - Horticulture, Clemson University. (New 02/08.)
Barklice are small and, with few exceptions, inconspicuous insects. They are members of the order Psocoptera, and there are over 300 species in 26 families in the United States and Canada. The vast majority of the species live outdoors in a variety of habitats. Barklice are soft-bodied insects usually less than ¼-inch in length with long antennae and two pairs of wings carried folded over their backs. They are common on trees, and some species construct quite conspicuous webs on the bark of the trunks and large limbs. Barklice undergo simple metamorphosis (meaning that the young resemble the adults) and pass through six nymphal stages (instars) before becoming adults.
A 'herd' of barklice on a tree.
Although these insects resemble aphids and are called "lice", they are not pests or parasites of either plants or animals. Since they aren't true lice, entomological convention requires that the name be written as a compound word instead of two words. They feed on a variety of foodstuffs such as mold, pollen, fragments of dead insects, algae, and lichens. Due to their inconspicuous nature, barklice often go unnoticed. However, two gregarious (staying together in large groups) species are often noted in the southeastern United States due to their activities. One species (Cerastipsocus venosus) found on the bark of trees moves as a group resembling a herd of animals or flock of birds. Another species (Archipsocus nomas) makes conspicuous silken webs on the bark of tree trunks and limbs. This webbing is most common in the coastal plain counties and appears in the late summer. The webbing from barklice is rarely found on the foliage, which differs from spider mites and certain caterpillars.
Barklice are harmless, and the webbing formed by some species does not harm the trees on which it occurs. The presence of barklice indicates that a suitable habitat for them exists. Since the tree-dwelling species eat fungus, lichen, and organic debris, they could be viewed as beneficial insects. Control of such insects is unnecessary; however, if you consider the webbing to be unsightly, you could use a high-pressure stream of water to remove it from the trees.
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