The subterranean termite - the type that does most damage to houses and other buildings - actually lives in the soil, not in the house.

They enter and attack wooden parts of the house only because this is the handiest source of food for the colony. They live on cellulose, the principal ingredient in wood. So houses and other structures made of wood provide the most readily available source of food when they cannot find enough in the ground near their nests.

They must also have moisture to exist, and this requires that they return to the soil each day - which is why all currently approved termite-proofing techniques involve poisoning the soil through which they must pass when entering and leaving the house.

There is never a need to worry about termites that are left in the wood after their access to the moisture in the soil is cut off; these will soon die (unless they can quickly locate another source of moisture, such as a leaking pipe).

Termites live in highly organized underground colonies that contain one or more reproductive queens and their kings, the workers that hunt for and bring back the food, and soldiers that protect the colony against attack by ants or other insects.

The workers do all the damage to buildings, fence posts and other wood structures. They never chew completely through a beam or piece of wood; instead they tunnel their way through the soft grain to create galleries or tunnels inside the wood. If they accidentally break through the surface they quickly draw back and plug the hole to protect themselves against the drying effect of the air.

They also have an uncanny ability to know just how much they can weaken a beam without causing it to a collapse or break, and always move on before this happens (when a collapse does occur it is almost always because somehow the load or tension on that member was increased after it was weakened by the termites).

When a colony develops beyond a certain size the potentially reproductive members of the colony (called nymphs) sprout wings and venture out in swams for the first and only time in their lives in a brief search for a site to establish a new colony. This short-lived swarming period ends when a site is found and the insects shed their wings to reenter the ground and set up their new colony.

Although the actual flight of the winged termites is not often observed by the homeowner (usually in the spring, but occasionally in the fall), the discarded wings are often seen near the place they entered, and this is a sure indication of an established termit colony nearby.

Often, however, a homeowner will spot a swarm of flying ants and mistake them for winged termites. Although at first glance they look alike, they are actually quite different and the differences are easy to detect. The termite's wings are all the same size while the ants have two smaller and two larger ones. Also, the ant has a two-part body connected by a narrow waist, while the termite's body is fairly straight along its full length. Fortunately, termites do not really work fast; it takes years for them to build a colony and do serious damage to a house nearby. That is why when signs of a termite infestation are discovered, either wings left after a swarming period, or actual signs of damage to some of the wood members in the house, there is no need to panic or act in haste.

If in doubt,probe the suspected wood with a knife or other sharp tool. It may seem solid on the outside, but will permit the tool to penetrate easily because the wood has been hollowed out on the inside. The best idea by far is to call a professional for a thorough inspection.

Whever possible, termites will enter the wood structure of a house by working their way through wood members in direct contact with the ground, so they can pass back and forth unnoticed and without beign exposed to the drying effedts of the light and air. However, just because there is no wood in direct contact with the ground does not mean they will be kept out. They often build mud tubes or tunnels along the face of a concrete foundation or along the outside of a metal or plastic pipe to get to the wood above without coming into the open.

Many cases have been documented where they build mud tubes straight up from the ground in crawl spaces or similar locations - even where there is no support for the tubes or tunnels - until the tube is high enough to permit them to enter wood beams above. Once completed, these tubes, which vary from 1/4-inch in width, serve as a means for the workers to travel back and forth each day while maintaining the warm damp atmosphere they require.

The method almost universally used to combat termite infestations is to poison the soil around the house with a chemical such as chloradane. When the soil is properly saturated, this chemical will kill termites on contact for years after application, and because the termites must pass through this barrier to reach the house, sooner or later they will be killed. Those trapped inside the house will die because they cannot survive without returning to the soil each day.

The usual procedure for poisoning the soil is either to dig a trench at least 30 inches deep, pour in the chemical and mix additional chemicals into the soil at close intervals with special pressurized equipment.

Although it is the theoretically possible for the homeowner to tackle this job on a do-it-yourself basis, most experts feel that few if any homeowners can do a really thorough job of termite-proofing; extensive digging and saturating the soil around the foundation is not always enough. Concrete slabs poured on the ground next to the house (porches, patios, driveways, etc.) must also have the soil underneath treated because termites can penetrate through tiny cracks and gain entry to the house.

The same is true for concrete stoops next to the house - and even for a concrete basement floor. If the soil underneith is not treated, a colony can continue to thrive and may gain entry through small cracks in the slab or footing.

It is for these reasons that professionals who are thorough will always drill through basement floors, adjoining concrete slabs and stoop or garge floors, so that the soil underneath can be treated by injecting the chemicals. The holes that are left are patched later.

This work can, of course, be done by the homeowner who is capable and can rent the needed equipment. In some areas the insecticide, such as chlorandane, is not available to the do-it-yourselfer, though many areas now sell it for treatment of termites only (it is not allowed for a general insecticide in gardens).

Avoid the temptation to treat only one area or section of the house because that is the only place termites have been found. Treating one part of the perimeter almost always results in merely postponing the complete job; when they cannot get through in one place, they will soon find another unprotected area through to enter.