Subterranean termites are social insects that live in nests or colonies in the soil, hence their name “subterranean.” These colonies contain three forms or castes: reproductives, workers and soldiers. Individuals of each caste have several stages: the egg; the larva that develops into a pseudergate and eventually into a brachypterous nymph or soldier; and the adult. Reproductive adults have three forms: primary, secondary and tertiary reproductive (Fig. 2).
Reproductive males and females can be winged (primary) or wingless (secondary or tertiary). Each can produce new offspring. The bodies of primary reproductives, also called swarmers or alates, vary by species from coal black to pale yellow-brown. Wings may be pale or smoky gray to brown and have few distinct veins. Swarmer termites are about 1/4 to 3/8 inch long.
Secondary and tertiary reproductives in the colony are generally white to cream-colored and may have short wing buds. Developed as needed, they replace a primary queen when she is injured or dies. They also develop in addition to the primary queen and lay eggs for the colony. Supplementary reproductives, including a group of males, workers and soldiers, may become isolated from the main colony and can establish a new colony.
Termite workers make up the largest number of individuals within a colony. Workers are wingless, white to creamy white, and 1/4 to 3/8 inch long. They do all of the work of the colony -- feeding the other castes, grooming the queen, excavating the nest and making tunnels. In working, they chew and eat wood, causing the destruction that makes termites economically important.
Soldiers resemble workers in color and general appearance, except that soldiers have large, well-developed brownish heads with strong mandibles or jaws. Soldiers defend the colony against invaders, primarily ants. In some types of termites generally occurring in arid regions, soldiers are called nasutes. Nasute soldiers have pear-shaped heads with a long, tube-like projection on the front. They exude a sticky substance to entrap their enemies.
It is important to be able to distinguish between swarming termites and ants (Fig. 3). They often swarm around the same time of year, but control measures for each differ greatly.
Biology and habits After a termite colony matures, which requires from 2 to 4 years, swarmers are produced. Swarming usually occurs from January through April, during the daylight hours, usually after a rain. Environmental factors such as heat, light and moisture trigger the emergence of swarmers. Each species has a definite set of conditions under which it swarms. The number of swarmers produced is proportionate to the age and size of the colony.
Both male and female swarmers fly from the colony and travel varying distances. They are extremely weak fliers; wind currents usually carry those that travel any distance. Only a small percentage of swarmers survive to develop colonies; the majority fall prey to birds, toads, insects and other predators. Many also die from dehydration or injury.
A pair that survives lands and immediately seeks cover under rocks or other materials. The pair makes a very small nest before mating. Initially, the new queen termite lays only a few eggs. The male, or king, remains with the female because periodic mating is required for continued egg development.
Eggs are not deposited continuously; in fact, only a few hundred are deposited during the first year. In subsequent years, the young queen grows larger and lays more eggs. Larvae hatch from the eggs within several weeks and are cared for by the new king and queen. The larvae molt into pseudergate workers, and then into presoldiers or brachypterous nymphs. The colony stabilizes when the queen reaches maximum egg production. If the queen dies, secondary reproductives take over the queen’s duties.
The maximum size of a colony depends on such factors as location, food availability and environmental conditions, especially temperature and moisture. Some colonies remain small; others contain up to several thousand individuals.
New colonies form when the old colony produces swarmers or when groups of termites become isolated from the main colony and establish subcolonies. This is called colony splitting. These subcolonies may exist independently or unite with the main colony.
Subterranean termites derive their nutrition from wood and other material containing cellulose. Paper, cotton, burlap or other plant products often are actively attacked and consumed by termites. Subterranean termites cannot digest cellulose directly. They depend on large numbers of one-celled animals (protists) living in the termite hind gut to break down the cellulose to simple acetic acid, which termites can digest. Worker termites and older nymphs consume wood and share their nourishment with the developing young, other workers, soldiers and reproductives.
Moisture is important to subterranean termites, which have very little resistance to dehydration. To survive, they must maintain contact with the soil (their primary moisture source) or other above-ground moisture sources, such as in structures with defective plumbing or guttering.
Subterranean termites also must protect themselves from temperature extremes and attack by such natural enemies as ants and other insects. Termites foraging for food above ground protect themselves with shelter tubes, which are sometimes called mud tubes (Fig. 4). Worker termites build the tubes from particles of soil or wood and bits of debris held together by salivary secretions. The tubes may be thinly constructed or large and thick-walled to accommodate many termites moving vertically between the soil and the food source.
This construction material also is found lining the galleries built in wood being attacked and aids in identifying termite-damaged wood. Shelter tubes often are used to bridge masonry or other objects, allowing termites access to a food source (wood) above ground.
Dead trees and brush are the original food source of subterranean termites. When land is cleared of this material and houses are built on these sites, termites attack the structures. Termites can enter buildings through wood in direct contact with the soil, by building shelter tubes over or through foundations, or by entering directly through cracks or joints in and under foundations.
Any material in direct contact with the soil -- such as trees, vines or plumbing fixtures -- serves as an avenue of infestation. Subterranean termite swarmers may also be blown into or on structures and then start a new colony.
Signs of infestation
The presence of swarmers, wings or damaged wood signals that termites are infesting a structure.
Swarmers: Generally, the first sign of infestation noticed by homeowners is the presence of swarming reproductives on window sills or near indoor light. Swarmers inside the house nearly always indicate an active infestation in the structure. The presence of swarmers outdoors is a natural phenomenon, but should warn that termites are near and possibly attacking a nearby building.
Wings: Another indication is the presence of wings, discarded by swarmers as a normal part of their behavior, found near emergence sites, on window sills or in cobwebs. Infestations also can be detected by the presence of shelter tubes going up the sides of piers, utility entrances or foundation walls.
Damaged wood: Wood damage often is not found initially, but it definitely indicates termite infestation. Any wood-to-soil contact is a potential site of entry into a home. Wood that yields a dull, thudding sound when struck by a screwdriver or hammer should be examined. Careful probing of suspected areas with a sharp, pointed instrument such as an ice pick will disclose termite galleries or damage.
Characteristics of damaged wood
Subterranean termite damage almost always is confined to the soft, springwood growth of the wood. Tunnels tend to follow the wood grain. They either are lined with the same material used to build shelter tubes, or have a pale, spotted appearance resulting from soft fecal material plastered on tunnel surfaces. Look for moisture sources that may cause wood decay, which can encourage subterranean termite infestation. Extensive deterioration from wood decay can be confused with termite damage.