Subterranean Termites
Forest Health Guide for Georgia Foresters
Written by Terry Price, Georgia Forestry Commission
Adapted for the web by the Bugwood Network
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Subterranean termites are by far the most destructive insects that attack wood in use. Ninety-five percent of all termite damage in the United States can be attributed to the eastern subterranean termite, Reticulitermes flavipes, (Figure 40). Infestations may occur in poles, woodwork of buildings, and occasionally in living trees, shrubbery and other plants. In recent years the Formosan termite, Coptotermes formosanus, has threatened North America
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Figure 40 - Heads of termite soldiers; Formosan-left, eastern subterranean-right
photo from USDA Forest Service - Wood Products Insect Lab Archives |
Figure 41 - Formosan termite soliders
photo from USDA Forest Service - Wood Products Insect Lab Archives |
(Figure 41). This termite was first reported from a shipyard warehouse in Houston, TX in 1965. Since then it has been reported from several southern and Gulf Coast states.
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Termites are commonly known as wood lice or white ants. They look somewhat like ants but do not have the constricted “waist”. Three different forms or “castes” of termites are usually present in a colony. The most numerous caste is the worker. These are small, white, wingless, soft-bodied insects that do the work in the colony. The soldiers are similar but have greatly enlarged heads and powerful mandibles. Their function is to protect the colony. The winged reproductive caste is the one
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Figure 42
photo from USDA Forest Service Archives |
most commonly seen. These are brown to black in color with 4 large fragile wings. They look like flying ants but all 4 wings are the same size while the front wings of the ants are larger than the hind wings (Figure 42). Winged adults swarm or emerge from older colonies in spring and occasionally in the late summer. These winged adults mate soon after swarming and search for a place to establish a new colony. Termite swarms are often the first indication of an infestation.
Although the swarm poses little or no immediate danger to the structure, it gives warning of termites in close vicinity. Earthen shelter tubes constructed over surfaces of foundation walls and directly connecting the soil and the structure are signs of termite infestation. These tubes are between one-fourth and one-half inch or more wide (Figure 43). If the tunnels or tubes are in use, the insides will be moist and there may be white workers present. If the tubes are not in use and have been abandoned, they will be dry and crumble easily.
Figure 43 - Termite mud tubes on fence post
photo by Terry Price |
Without the external evidence of winged termites or visible shelter tubes, it is more difficult to determine whether or not termites are present in a building. The first place that should be checked is wood that is near or rests on the ground. Weather boarding, wood supports, basement window frames, door casings, sills, etc. can be checked for soundness by being tapped with a hammer and probed with a screwdriver or ice pick. If hollow wood is found, and it is the result of a termite infestation, the soft portions of the wood will be eaten leaving the hard sections. Also, accumulations of a wood type paste and excrement are often present.
Preventative measures to protect a building against subterranean termites are best when done during the construction. Since termites are present in their
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natural habitats, all stumps, roots, fallen trees and other wood debris should be removed from the building site prior to beginning construction. All scraps of lumber should be removed and not buried beneath porches, terraces, carports, around foundations, etc. There is less likelihood of the building being infested when no wood is left on or buried in the soil.
The basic principal of preventing and controlling an infestation of termites is the insulation of woodwork from the ground. To accomplish this special care is needed in design and construction near or below grade level so termites do not have an easy and convenient way to reach the wood. The addition of termite shields may give some degree of protection, however, experience has shown that good shield construction and installation are rare. Protection of woodwork in construction may be supplemented by the use of chemicals as soil poisons. Treating the soil with an effective insecticide before and during construction is the best means of assuring a complete chemical barrier below and around a structure. At this time crawl spaces and basements are exposed for thorough treatment before the concrete slab or floor is poured, foundation walls are not capped, and there is no need to drill and dig special trenches.
Lumber should be stacked above ground with all supports chemically treated to prevent infestation by termites. Termites often infest trees recently attacked by pine bark beetles.
The Formosan termite does not have to maintain a contact between the wood and the ground, therefore, soil treatment with an insecticide is not always effective against this pest. Colonies have been observed in living and dead trees, on boats and ships and in floating drydocks. Fumigation is often required to control infestations of Formosan termites.
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