Termites comprise a large and diverse group of ecologically and economically important insects that feed on cellulose, principally in wood. Worldwide there are over 2,600 species of termites. Although many people associate termites with negative impacts, in nature they make many positive contributions to the world's ecosystems.
Termites commonly feed on felled trees and stumps, grasses, bushes, or other pieces of dead or decaying wood. Termites can be highly beneficial as they degrade woody debris, return nutrients to the soil, and provide an energy-rich food source to a variety of predators. Their tunneling efforts help to ensure that soils are porous, contain nutrients, and are healthy enough to support plant growth. Termites rarely injure or kill trees. However, a minority of termite species can be very destructive to wood in buildings, including furniture and many other wood-based products. Each year thousands of housing units require treatment for the control of these insects.
Dampwood termites are common throughout the state; however, due to high moisture requirements, they are most often found in cool, humid areas along the coast. They typically infest decayed wood that remains moist either through contact with the soil or exposure to a water leak. Dampwood termites create large, open galleries within the wood where they live and feed. Their presence is significant as an indicator of a moisture problem or wood decay in wooden structures.
All species of drywood termites infest dry, sound wood-including structural lumber, dead limbs on trees, utility poles, decks, fences, lumber in storage, and furniture. From this infested wood, winged reproductives periodically swarm to infest additional nearby wood. Drywood termites are most prevalent in desert areas, but also occur along most coastal regions and in the Central Valley. Nests of most species remain entirely above ground and do not connect to the soil.
Similar to dampwood termites, feeding by drywood termites can cut across the grain of wood leaving a characteristic pattern of chambers and tunnels, some of which are filled with fecal pellets. Drywood termites often expel their fecal pellets through surface openings and they can accumulate on horizontal surfaces below the openings. These fecal pellets, which are distinctive in appearance with six longitudinal flattened sides, may be the first clue to their presence. For further information on drywood termite biology and management see Pest Note: Drywood Termites.
Building design may contribute to the probability of termite invasion. Identify and correct any structural deficiencies that attract or promote subterranean termite infestations. Ideally all substructural wood beneath the building should be kept at least 12 inches above the soil. Consult local building codes for exact, minimum distances from wood to soil. Stucco siding that reaches the ground may promote termite infestations since termites might travel between the stucco and the foundation unseen. Keep foundation areas well ventilated and dry. Reduce chances of infestation by removing any wood in contact with the soil. Inspect porches and other structural or foundation wood for signs of termites. Look for tree stumps, stored lumber, untreated fence posts, and buried scrap wood near the structure that may contribute to a termite infestation.
Structural lumber in buildings is usually Douglas-fir, hemlock, or spruce. Of these materials, Douglas-fir is moderately resistant to termites, whereas the other two are not. Lumber used in foundations and other wood in contact with the soil should be chemically treated or naturally resistant to termites and decay to help protect against termite damage in areas where building designs must be altered or concrete cannot be used. When using naturally resistant wood species, we recommend that you request documentation from suppliers to authenticate resistance levels stated on labeling. If susceptible wood is used above the treated wood, however, subterranean termites can build their shelter tubes over chemically treated wood and infest untreated wood above.
Subterranean termites in structures cannot be controlled using techniques that are appropriate for drywood termites, such as fumigation, heat treatment, freezing, and termite electrocution devices, because the reproductives and a large majority of the termites are concentrated in nests near or below ground level out of reach of these control methods. The primary methods of controlling these termites are insecticides, either applied to the soil adjacent to the structure, directly to nests via shelter tubes, or through bait stations. To facilitate control of subterranean termites, destroy their shelter tubes whenever possible to interrupt access to wooden substructures.
Liquid applications of pesticides are most often used for subterranean termite control and applied to the soil either in drenches or by injection. There are no reliable over-the-counter termite control products available for the public, all effective products are for professional use only.
Pest management professionals are provided special training because of the hazards involved in applying insecticides to the soil around and under buildings. Applications in the wrong place can cause insecticide contamination of heating ducts and/or damage to radiant heat pipes or plumbing used for water or sewage under the treated building. Soil type, weather, and application techniques influence the mobility of insecticides in the soil; soil-applied insecticides must not leach through the soil profile to contaminate groundwater or run off to contaminate surface water.
Recently, active ingredients used to control subterranean termites in soils were broadly classified as repellent or nonrepellent. Subterranean termites can detect repellent insecticides, usually pyrethroids; and they are repelled without receiving a dose that would kill them. Because of this negative reaction, termiticide products containing repellent active ingredients have been phased out.
Newly introduced chemicals are available that are less toxic to humans and other mammals than the older insecticides but remain highly toxic to insects. These insecticides, including chlorantraniliprole, fipronil, and imidacloprid are nonrepellent to termites and have been shown to be effective in killing termites at low dosage rates under climatic conditions. Depending on the label language, these materials are used as barriers as described above and also as local treatments, targeting nests directly via shelter tubes.