Termites are rarely seen directly, which means recognizing a termite infestation depends almost entirely on reading the physical evidence they leave behind. The signs vary significantly depending on species: subterranean termites signal their presence through mud tubes, moisture-related wood damage, and swarm events, while drywood termites are most reliably identified by frass piles and kickout holes in wood surfaces. Knowing which signs to look for, where to look, and what each sign means determines how quickly and accurately you can confirm an infestation and decide on a treatment approach.
Mud Tubes on Foundation Walls and Structural Members
Mud tubes are the single most reliable indicator of subterranean termite activity in or near a structure. Subterranean termites build these pencil-width tunnels from soil, saliva, and wood particles to connect their underground colony to the wood they are feeding on above the soil line. They require high humidity to survive outside the soil, and the mud tube maintains that environment as they travel. Mud tubes are most commonly found running up foundation walls, across concrete piers, along floor joists in crawl spaces, and in some cases up interior walls where the termites have reached above-grade wood.
To test whether a mud tube indicates an active infestation, break a small section of it open. Active workers will be visible inside, or the tube will be repaired within a few days. A dry, hollow, unrepairable tube suggests the colony has abandoned that foraging route, though the structure may still be infested elsewhere via separate tubes. Mud tubes that show no repair activity after a week of monitoring may indicate a past infestation rather than a current one, but it is worth continuing to inspect surrounding wood for damage before ruling out ongoing activity.
Frass: The Drywood Termite Sign
Frass is the fecal material that drywood termites push out of their galleries through small openings called kickout holes. Unlike subterranean termite frass, which is incorporated into mud tubes, drywood termite frass is dry and pellet-shaped, with a distinctive hexagonal cross-section that is visible under magnification. The pellets are roughly the size of a sesame seed and vary in color from cream to dark brown depending on what wood the termites are feeding on.
Frass piles accumulate directly below kickout holes, typically appearing as small conical mounds on floors, windowsills, furniture, or baseboards. The kickout hole itself is tiny, usually only about 1 mm in diameter, and is often sealed with a thin membrane that the termites periodically open to clear accumulated frass. Locating the kickout hole above a frass pile helps identify exactly where the drywood termite colony is active in the wood, which is essential information for targeted treatment. The full DIY treatment approach for drywood termites, including foam injection and boron-based products, is covered in the drywood termite guide.
Discarded Wings After a Swarm
Termite swarms produce winged reproductives called alates that leave the colony in large numbers, typically during warm days in spring or early summer following rain, or in late summer for drywood species. After mating, the alates shed their wings and attempt to found new colonies. Finding piles of discarded wings near windowsills, doorways, vents, or light fixtures is a strong indicator that a swarm has occurred and that an established colony is nearby, either inside the structure or in close proximity to it.
The wings themselves are an important identification tool. Termite alates have four wings of equal length, and all four wings are the same size. Flying ant alates have two large front wings and two smaller rear wings, a pinched waist, and distinctly elbowed antennae. This difference matters because flying ant swarms are commonly mistaken for termite swarms, and the treatment decisions that follow are completely different. The visual differences between the two are covered in detail in the termites versus flying ants comparison.
Hollow-Sounding and Visually Damaged Wood
Termites consume wood from the inside out, leaving a thin outer shell that can appear intact while the interior is heavily hollowed. Tapping wood surfaces with a hard object produces a distinctly hollow sound where termite galleries are present, compared to the solid sound of undamaged wood. This is a practical diagnostic technique for checking baseboards, window frames, door frames, floor joists, and wall studs in areas where other signs have been found.
In more advanced infestations, the wood surface itself shows visible damage. Blistered or darkened patches on wood floors or painted trim can indicate termites feeding just below the surface. Wood that has been structurally weakened may flex or compress under light finger pressure where it would normally be rigid. Tunnels or galleries running parallel to the grain may be visible if a piece of suspect wood is cut open or probed with a screwdriver or awl. Any visible structural damage to load-bearing members warrants a professional inspection before treatment begins, to assess whether repair is needed alongside control.
Sagging Floors, Buckling Ceilings, and Loose Tiles
Structural damage from a long-running termite infestation often produces secondary effects that homeowners notice before they identify the termite activity itself. Floors that have developed a soft spot, slight sag, or bounce in a localized area may have had the subfloor or the joists beneath weakened by termites. Ceiling sections that have developed a bow or stain, particularly in lower floors of a multi-story home, can indicate termites moving through the framing above. Loose or raised ceramic tiles in bathrooms or kitchens can result from subterranean termites introducing moisture under the adhesive layer as they move through the subfloor.
These structural signs are worth investigating proactively rather than attributing them to settling or moisture without ruling out termite activity. A termite infestation that has progressed to the point of producing structural symptoms has typically been active for several years, meaning the colony is established and a treatment decision is overdue.
Where to Inspect for Termite Activity
A systematic inspection covers both the exterior and interior of the structure. On the exterior, check the foundation perimeter for mud tubes, inspect where any wood elements contact soil such as deck posts, fence bases, and wood siding at grade, and look along the roofline for swarm debris or damaged wood. On the interior, the most productive areas are the crawl space if one is present, the basement or slab perimeter, around plumbing penetrations where moisture may be elevated, window and door frames on lower floors, and any areas where a previous moisture problem such as a plumbing leak or roof leak has occurred.
Termites are reliably attracted to moisture-damaged wood because it is easier to consume and the conditions suit their survival requirements. Any area of a structure that has had prior water damage is worth inspecting carefully even if it has been repaired, since wood that was softened by moisture may have been colonized before or during the repair. Monitoring stations placed in the soil around the perimeter also function as early detection tools: they attract foraging workers, and checking them periodically reveals subterranean termite activity in the soil before the insects reach the structure. The best termite bait stations guide covers monitoring and treatment station options.
What to Do Once You Find Signs
Confirming the species is the priority after finding signs, because the treatment approach for subterranean and drywood termites is fundamentally different. Mud tubes point to subterranean termites, and treatment focuses on a soil barrier or bait system. Frass and kickout holes point to drywood termites, and treatment focuses on localized wood injection or, for widespread infestations, professional fumigation. An overview of how to match signs to species and select the appropriate DIY treatment method is in the how to get rid of termites guide. For an overview of all the hubs and resources in this silo, return to the termite hub index.