A termite colony inside your house can range from a few thousand insects quietly eating through a single beam to several hundred thousand workers tunneling through walls, floors, and structural framing. The average mature subterranean termite colony contains roughly 300,000 members, though some reach into the millions. A colony of just 60,000 workers can consume a foot of standard 2×4 lumber in about five months. That sounds slow, but the damage compounds over years, and most homeowners don’t discover a colony until it has been active for a long time.
Types of Colonies That Infest Homes
The type of termite colony in your house determines where the damage is, how it got there, and how it’s treated. Three types are responsible for most residential infestations in the United States.
Subterranean termites are the most common and destructive. They live in the soil and build mud tubes (pencil-width tunnels made of dirt and saliva) to travel between the ground and the wood in your home. They prefer soft springwood, leaving behind galleries that contain soil and have a layered, rough appearance with alternating damaged and undamaged wood. These colonies need constant moisture from the soil, which is why they maintain that connection to the ground.
Drywood termites live entirely inside the wood they eat, with no soil contact at all. The wood itself provides enough moisture for them to survive. They tend to nest under wooden roof shingles, eaves, or siding, and they eat through both soft and hard wood, carving smooth, sculptured galleries. A telltale sign is small fecal pellets, about the size of sand grains, that accumulate below infested wood or on windowsills.
Formosan termites are a particularly aggressive subterranean species. They also consume both soft and hard wood like drywood termites, but their galleries contain neither fecal pellets nor soil. Formosan colonies can grow extremely large and cause damage faster than other species.
How Termites Get Inside
Subterranean termites don’t just appear in your house. They get there through a predictable sequence: underground foraging tunnels reach your foundation, workers find a crack or gap, and they build mud tubes from that entry point to the nearest wood. Workers can squeeze through an opening as small as 1/32 of an inch, which means expansion joints, settling cracks in the slab, gaps around plumbing pipes, and bath trap openings are all viable entry points.
Slab-on-ground construction is the most vulnerable foundation type. Workers build mud tubes on pipes or conduit that penetrate the slab, and in crawl spaces, they sometimes construct free-hanging “drop tubes” that extend from the ground up to floor joists. Any place where wood siding extends below the soil line creates a hidden highway: termites can travel behind the siding without ever building a visible mud tube.
Outdoor wood structures connected to your house also serve as bridges. A trellis against an exterior wall, a planter box, or a wooden porch railing can all become pathways. Termites infest the outdoor wood first, build mud tubes through it, and eventually find a crack or gap that leads inside.
Once inside, groups of termites can sometimes become separated from the main colony in the soil. If they find a moisture source like a roof leak or a dripping pipe inside a wall, they can establish what’s called a secondary colony. These above-ground colonies are self-sustaining: they reproduce, grow, and consume wood without ever needing to return to the soil. Secondary colonies are sometimes found on upper floors of homes, far from the foundation.
Signs of an Active Colony
Termite colonies are designed to stay hidden. Workers avoid light and open air, so visible damage usually means the infestation has been progressing for a while. The most recognizable signs depend on the species.
For subterranean termites, look for mud tubes on foundation walls, piers, pipes, or along baseboards. These tubes are typically brown, roughly the width of a pencil, and may appear on interior or exterior surfaces. Tap wood that you suspect is infested. Hollow-sounding or soft wood, particularly near the floor level, is a strong indicator. You might also notice bubbling or peeling paint that looks like water damage, or small holes in drywall.
For drywood termites, the signature clue is piles of tiny, six-sided fecal pellets below infested wood. These pellets are hard, dry, and often a tan or dark brown color. You might find them on windowsills, countertops, or floors beneath wooden beams.
Both types produce winged reproductive termites (called swarmers) that leave the colony to start new ones. If you see a swarm of small winged insects inside your house, or find discarded wings near windows and light fixtures, there is almost certainly an active colony nearby. Subterranean swarmers typically emerge in spring, while drywood swarmers often appear in late August and early September.
How Professionals Find Hidden Colonies
Much of the damage a termite colony causes is behind walls, under floors, and in places you can’t see. Professional inspectors use a combination of traditional and technology-based methods to locate activity without tearing open your walls.
The standard toolkit includes a flashlight, a tapping tool (used to check timber for hollow spots and soft areas), and a moisture meter. These catch many infestations, but they rely on damage being advanced enough to detect by sound or touch. Thermal imaging cameras can find colonies much earlier. Termites actively regulate the temperature and humidity inside their galleries, and that creates small temperature differences on the surface of walls, ceilings, and floors. A thermal camera picks up those differences, allowing an inspector to scan large areas quickly, including hard-to-reach spots like high ceilings and behind built-in cabinetry.
Thermal imaging is especially useful for spotting secondary colonies in upper stories and interior walls, where there may be no visible mud tubes or other surface evidence.
Treatment Options for an Active Colony
There are two main professional approaches to eliminating a subterranean termite colony in your house, and the right choice depends on the species, the extent of the infestation, and your home’s construction.
Liquid Soil Barriers
This is the traditional method. A pest control company injects large volumes of liquid termiticide into the soil under and around your home’s foundation, creating a chemical barrier that termites cannot cross. Workers trying to pass through treated soil are killed, and those already inside the house are cut off from the colony and eventually die. Modern products are non-repellent, meaning termites don’t detect the chemical and walk through it rather than routing around it. This makes the barrier significantly more reliable than older repellent products. Treatment involves drilling through adjacent porches, patios, and slabs to inject the termiticide beneath them.
Baiting Systems
Bait stations take a different approach. Small plastic stations are installed in the ground around your home’s perimeter, typically 10 to 15 feet apart and about 1 to 2 feet from the foundation. Each station contains cellulose (wood-based material) combined with a slow-acting substance that disrupts the termites’ ability to molt. Workers eat the bait, carry it back to the colony, and share it with nest mates. Over weeks, the colony population gradually declines. The slow action is intentional: if termites died immediately near the stations, other workers would learn to avoid them. Stations can also be placed indoors directly over active mud tubes. Ongoing monitoring and re-baiting is part of the program, since the goal is to maintain a termite-free perimeter over time.
Drywood Termite Treatment
Because drywood termites live entirely within the wood and have no soil connection, soil barriers and ground bait stations don’t work against them. Localized infestations can sometimes be treated by injecting termiticide directly into the infested wood. Widespread drywood infestations typically require tent fumigation, where the entire structure is sealed under a tarp and filled with gas that penetrates the wood.
Damage Repair Costs
The financial impact of a termite colony depends heavily on how long it’s been active. Extermination itself typically costs between $250 and $1,000 for an average infestation. The real expense is repairing what the colony has already eaten.
Termite damage repair averages about $3,000, but the range is wide. Minimal damage, like a few compromised boards or joists, runs $250 to $1,000 to fix. Medium-scale damage to walls, flooring, or framing falls in the $1,000 to $3,000 range. If the colony has reached major structural components like beams or load-bearing walls, expect $3,000 to $10,000 or more. Replacing a single rotted beam costs $1,500 to $5,000. If termites have damaged electrical wiring inside walls, basic outlet and wiring repairs add $130 to $350 per location.
Preventing a Colony From Establishing
The single most important prevention measure is eliminating direct contact between wood and soil. Wood siding, door frames, and window frames should sit at least six inches above ground level. If your home has latticework, porch steps, or deck posts that touch the soil, those are high-risk entry points. Even pressure-treated wood is vulnerable: termites enter through cracks and cut ends, or simply build tunnels over the treated surface.
Moisture is the other major factor. Subterranean termites are drawn to consistently damp soil near foundations. Make sure gutters and downspouts direct water away from the house, fix any leaking outdoor faucets or pipes, and grade the soil so surface water slopes away from the foundation. Lawn sprinklers aimed at or near the foundation create exactly the conditions termites prefer.
In crawl spaces, ventilation and moisture barriers make a significant difference. Building codes generally call for one square foot of vent opening per 150 square feet of crawl space. At least one vent should sit within three feet of each exterior corner. Laying 4 to 6 mil polyethylene sheeting over about 75 percent of the exposed soil acts as a vapor barrier, reducing evaporation and condensation on joists and subflooring. Keep vents clear of leaves, dirt, and vegetation that could block airflow.
None of these steps guarantee you’ll never get termites, but they remove the conditions that make your home an easy target. A colony needs food, moisture, and a hidden path inside. Eliminating even one of those makes your house far less attractive than the next one down the street.