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Bark lice or psocids are small soft bodied insects which are often seen in groups or tiny herds on the surface of tree bark where they feed on lichens, fungi, and other superficial plant materials. They are members of the insect order, Psocoptera. The species Cerastipsocus venosus is one of the most common of the species that occur in Maine and can often become very abundant. These psocids appear in July as patches of tiny tan specks on the bark of various hardwoods and conifers. Individuals are less than 3/16 inches (5 mm) long. They can also be found on rocks, fence posts, picnic tables, etc. As they mature they turn gray with lighter cross-banding. Adults have dark smokey-gray wings with a triangular light spot on each forewing. The wings are held roof-like and almost vertically over the body at rest, and the psocids bear some resemblance to aphids. However, unlike aphids which possess a beak for sucking plant juices, psocids have chewing mouth parts. The young live in the same manner as adults; differing principally in the lack of wings which develop in pads on the back during later stages.

Adult females deposit their eggs singly or in small clutches on the bark or wherever the group finds its food, and cover each mass with a series of tiny silk strands. Psocids usually disappear soon after they develop wings in mid to late August. Winter is spent in the egg stage.

Bark lice feed on lichens and fungi on the tree bark and not on the tree itself. Since they cause no damage controls are not necessary.

Maine Forest Service - Forest Health and Monitoring Division - April 2000

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