1. Mud tubes on foundations, piers, or walls
Pencil-width brown tubes climbing a concrete foundation are the signature of subterranean termites — the most destructive group in the US. They travel inside these tubes because their bodies dry out quickly in open air. Break a section open: live termites inside confirm an active colony; a dried-out empty tube only means termites passed through at some point. Either way, check again after a week — rebuilt tubes mean activity.
2. Swarmers or discarded wings
Winged reproductives emerge in spring (subterranean) or late summer/fall (drywood), usually after rain. Piles of equal-length translucent wings on windowsills are the classic indoor clue. Swarmers inside your living space strongly suggest a colony in the structure; a swarm emerging from a stump 30 feet away may not.
3. Hollow-sounding wood
Tap baseboards, door frames, and window sills with a screwdriver handle. Termite-damaged wood sounds papery or hollow because workers eat the springwood between grain lines, leaving the darker summerwood as a thin shell.
4. Frass — drywood termite droppings
Drywood termites (common in coastal southern states and attics) push their six-sided, sand-like droppings out of small kick-holes. Look for tiny piles resembling pepper or fine sand below window sills, on spider webs in the garage, or in attic corners. Unlike carpenter ants, termites do not leave sawdust — frass is pelletized.
5. Blistering or "water damaged" paint
Paint that bubbles or peels with no leak underneath can be termites working just beneath the surface. The catch: moisture damage looks similar. Probe it — termite galleries are packed with mud-like material, while water damage leaves stained, crumbly fibers.
6. Tight-fitting doors and windows
Termite moisture and tunneling warp frames. It is the most often-missed sign because everyone blames humidity. If one door sticks but its twin on the same wall opens fine, probe that frame.
7. Sagging floors or ceilings
Late-stage subterranean damage shows as floor boards that flex, tile that pops, or a ceiling with a new sag. By this point the colony has been feeding for years — treat it as an emergency, not a DIY weekend.
8. Damaged wood with mud inside the tunnels
Any exposed damaged wood tells you who did it: termites pack galleries with soil and have a rough, muddy texture following the grain; carpenter ants excavate clean, smooth, sandpapered galleries and never eat the wood; wood-boring beetles leave round exit holes the size of a pinhead to a BB. If you are unsure, compare photos in the wood decay vs termite checker.
9. Clicking sounds inside walls
Soldier termites bang their heads against wood to warn the colony — a faint clicking from inside a wall at night in a quiet room is a real, if less common, sign. Put your ear to the wall near suspected activity and turn everything off.
What to do next
If any two of these signs are present, stop probing and price the fix. Treatment choice (liquid barrier, bait stations, fumigation for drywood) depends on the termite group, construction, and infestation spread — this is the one pest where professional treatment is usually worth it. Estimate your cost with the termite treatment cost estimator, and see whether the damage is actually moisture with the wood decay vs termite checker. For official identification help, your state's cooperative extension office — find yours via the USDA extension directory — and the EPA's termite identification guide are the authoritative starting points.
Prevention that actually reduces risk
- Keep soil, mulch, and firewood at least 6 inches below any wood siding and 12+ inches from the structure.
- Fix downspouts and grading so water drains away from the foundation — subterranean termites follow moisture.
- Replace exterior wood-to-ground contacts (fence posts, deck supports) with treated or non-wood materials.
- Get an inspection every 1–3 years in termite-prone states — most damage in swarming states is found during routine inspections, not by homeowners.
Sealing entry points and managing moisture are the two highest-value moves. Termites do not march across open concrete by choice — they follow damp soil and wood-to-earth contact into your home.