Updated July 13, 2026 · HomeFixx Editorial Team

Symptoms: What You're Seeing

• Mud tubes on foundation: Pencil-width tunnels of dirt and saliva running up your foundation walls, piers, or siding — usually found in crawlspaces, behind shrubs, or at slab edges where soil meets wood framing. Snap one open and you'll often find live worker termites inside. A tube that's dry and crumbly with no termites inside may be abandoned, but don't assume the colony is gone — it likely relocated to a different entry point nearby and is still active somewhere on the property.
• Hollow-sounding wood: Tap baseboards, sill plates, or porch posts with a screwdriver handle and they sound papery or hollow instead of solid. Termites eat wood from the inside out along the grain, leaving a thin veneer that crumbles under light pressure. If the screwdriver tip sinks in easily or breaks through the surface, that section has likely lost most of its structural integrity and needs immediate evaluation by a contractor, not just pest control.
• Discarded wings near windowsills: Piles of translucent, uniform-length wings — about 3/8 inch — collect on windowsills, in spiderwebs, or along baseboards each spring. Swarmers shed these wings within minutes of landing to start a new colony nearby. Finding wings indoors, as opposed to on an exterior windowsill or porch, is a stronger signal since it usually means the swarm originated from a colony already established inside a wall void or under the slab.
• Frass that looks like coffee grounds: Small mounds of pellet-shaped droppings, tan to black in color, pile up beneath wood trim, in attic corners, or near window frames. This is a signature sign of drywood termites, which don't build mud tubes. Because drywood colonies don't need soil contact, frass can appear in upper-floor window casings or attic rafters far from ground level, which is why many homeowners mistake it for sawdust from a DIY project rather than an active infestation.
• Tight-fitting doors and windows: Doors and windows suddenly stick or won't close flush, and paint or drywall shows subtle rippling or bubbling. Termite tunneling and moisture buildup inside the wood cause it to warp before any visible tunnel is found. This symptom is easy to blame on humidity or seasonal house settling, so pair it with a screwdriver tap test on the surrounding frame before assuming it's just weather-related swelling.

What's Actually Causing This

• Wood-to-soil contact: Any untreated wood — deck posts, fence posts, siding, or door frames — touching bare soil gives termites a direct highway into your structure with zero barrier. I see this on roughly 4 out of 10 termite calls, almost always where a deck or porch was built without a concrete footing or metal standoff bracket. Even pressure-treated lumber isn't immune long-term, since the treatment only protects the outer layer and termites can still exploit cut ends, screw holes, or weathered surfaces where the chemical barrier has broken down.
• Excess moisture around the foundation: Termites need consistent moisture to survive, and leaking gutters, poor grading, or AC condensate lines dumping water next to the foundation create the damp soil they're drawn to. Subterranean termites, the most destructive species in the U.S., build mud tubes specifically to maintain that humidity as they travel above ground. A single AC unit draining directly onto mulch or soil against the foundation can keep that spot damp nearly year-round in humid climates, effectively creating a permanent watering station for a colony.
• Mulch piled against siding: Wood mulch stacked more than an inch or two against the house acts like a termite buffet and moisture trap simultaneously. I've pulled active colonies out of mulch beds where homeowners piled it 6-8 inches deep right against vinyl siding, giving termites cover to feed undetected for years. Fresh mulch delivered annually without removing the old layer underneath compounds the problem, since the decomposing bottom layer retains moisture even during dry spells and stays warm enough to support termite activity through mild winters.
• Cracks in the foundation and slab: Hairline cracks as small as 1/32 inch in poured concrete or gaps around plumbing penetrations give subterranean termites a hidden route from soil to wall cavities. Older homes built before 1990 without a termiticide-treated soil barrier account for a disproportionate share of the repeat infestations I get called back to. Expansion joints and control joints, which are designed into the slab intentionally, are frequent entry points too, since builders rarely seal them with anything termite-resistant once construction wraps up.

Step-by-Step Diagnosis

Work through these steps before calling a contractor. Each step tells you what to look for and what it means.