Question: Something is making webs
all over the trunk of my tree. Is this doing damage? Should I
try to kill the spiders or whatever is doing this?
Answer: These webs are harmless and
are being caused by barklice rather than spiders. Barklice occur
on the trunks of a number of trees where they feed on lichens,
molds and fungi growing on the bark. Therefore, they may actually
be considered to be beneficial insects since they perform the
service of cleaning the trunks of trees.
Species belonging to two families of barklice
are commonly encountered in Texas: Psocidae ant Pseudocaecilliidae.
Psocidae are about 1/4 of an inch long and are black in color.
They live in clusters on the bark made up of many individuals
in similar stages of development. Consequently, tight clusters
of wingless immatures and clusters of winged adults located on
the trunks of trees such as Arizona ash are encountered at about
eye level. From a distance these clusters often look like knotholes.
The aggregated clusters of barklice move like herds of cattle
on the bark.
The Pseudocaeciliitae are much smaller in
size, duller in color and adults bear wings. The species most
noticeable, Archkipsocus nomas Gurney, makes unsightly silken
webs on tree trunks and branches These webs can completely wrap
a tree's trunk to the tips of each branch. Underneath this protective
webbing, the barklice feed on lichens and fungi. Host trees commonly
include oaks and pecans, although any tree with lichen and fungal
growth on the bark can support a barklouse population. Silk-wrapped
trees harboring this barklouse appear to occur at specific periods
of the summer (July and August) when conditions are favorable
for their development. The appearance of webbing often causes
concern to homeowners and landscape maintenance personnel that
are not familiar with this insect.
Pseudocaeciliid barklice are harmless to
trees and no insecticides are recommended for their control. Once
silken webbing appears, it will not be removed by chemical treatments.
If removal of the silk is desired, it may be
removed using spray of water under high pressure. Left undisturbed,
these barklice apparently remove the silken webbing at the end
of the summer. However, an observation has been made in pecan
orchards that the use of
fungicides will kill lichens. Lichens are, of course, symbiotic
associations of an algae and a fungus. One cannot survive without
the other. Without lichens, barklice will have nothing on which
to feed and thus populations will fail to develop.