Wood-destroying insects leave distinct physical evidence that you can spot before serious structural damage occurs. The main culprits are termites (subterranean and drywood), powderpost beetles, carpenter ants, and carpenter bees. Each one leaves different calling cards: mud tubes, frass piles, exit holes, or staining. Knowing which signs belong to which insect helps you understand the severity of the problem and what kind of treatment you’re looking at.
Subterranean Termite Signs
Subterranean termites live underground and build mud shelter tubes to travel between the soil and the wood they’re eating. These pencil-width tubes run up foundation walls, support piers, and plumbing under the house. They’re the single most recognizable sign of a subterranean termite problem, and finding even one active tube means the colony has established a direct highway into your structure.
Inside the home, the signs are subtler. BB-sized spots of dried mud on walls or ceilings (called pinholes in the pest control industry) appear when termites accidentally cut through to the surface and quickly patch the opening. You may also notice narrow, sunken winding lines in paint, wallpaper, or drywall. Termites eat the cardboard backing of sheetrock without disturbing the thin coat of paint on the surface, so the damage shows up as faint rippling or sagging in what looks like an intact wall.
Swarmers are winged reproductive termites that emerge in large numbers, typically in spring. Finding swarmers inside your home, or piles of shed wings on windowsills and floors, is a strong indicator of a nearby colony. A few stray swarmers that drifted in from outside aren’t necessarily alarming, but large numbers emerging directly from walls, ceilings, or floors point to an active infestation within the structure itself.
If you pull back damaged wood, subterranean termite galleries will contain dried mud or soil. This is a key distinction: wood rot can produce similar-looking damage, but termite galleries have that telltale dirt packed inside them.
Drywood Termite Signs
Drywood termites live entirely inside the wood they consume, with no connection to the soil. Their most distinctive sign is fecal pellets, often called frass. Under magnification, each pellet has a six-sided oblong shape and is relatively uniform in size. Color ranges from light tan to dark brown depending on the type of wood being eaten. At normal viewing distance, these pellets look like dust or fine debris and are easy to overlook.
Drywood termites solve their waste problem by cutting small “kickout holes” to the outside of the wood and pushing pellets out. You’ll typically find tiny piles of what looks like coarse sand or coffee grounds accumulating on surfaces below infested wood, often on windowsills, countertops, or floors. The pellets feel fine and gritty between your fingers. If you spot a small, clean hole in wood with a cone-shaped pile of uniform granules beneath it, drywood termites are the likely cause.
Powderpost Beetle Damage
Powderpost beetles leave small, round exit holes scattered across the wood surface, roughly 1/32 to 1/16 inch in diameter. These appear when adult beetles chew their way out after developing inside the wood as larvae. The holes are often described as “shot holes” because they look like the wood was peppered with tiny BBs.
The frass powderpost beetles produce varies by species. Lyctid beetles create frass that looks and feels like talcum powder, extremely fine and silky. Anobiid beetles produce frass that’s still powdery but has a noticeably gritty texture. Either way, you’ll often see this fine dust sifting out of exit holes or accumulating below infested wood.
The two main groups also target different woods. Lyctid beetles attack only hardwoods like oak, ash, hickory, and maple, making them a common problem in antique furniture, hardwood floors, cabinets, and interior trim. Anobiid beetles go after softwoods like spruce, pine, and fir, which means they can damage structural lumber including floor joists and wall studs. This distinction matters: an anobiid infestation in structural framing is a more urgent problem than lyctid beetles in a piece of trim.
Carpenter Ant Evidence
Carpenter ants don’t eat wood. They excavate it to build nesting galleries, and the debris they push out looks completely different from termite frass. Carpenter ant frass is coarse and fibrous, similar to pencil-sharpener shavings mixed with fine sand. It contains wood particles, insect body parts (legs, antennae, fragments of dead colony members), fecal matter, and sometimes soil particles. The color ranges from tan to medium brown in fresh softwood, and dark brown to near-black in decayed timber.
The galleries themselves are a giveaway if you can see exposed damage. Carpenter ant tunnels are clean, smooth, and dry, with an almost polished appearance. Termite galleries, by contrast, are rough and packed with mud or soil. Fresh frass deposits accumulate beside small kick-out holes in wood, building up in small piles roughly a quarter inch deep.
Carpenter Bee Holes and Staining
Carpenter bees drill nearly perfectly round entrance holes approximately half an inch in diameter into unpainted or weathered wood. The hole penetrates half an inch to one inch straight into the wood across the grain, then turns at a right angle to follow the grain for six to eight inches. Fascia boards, deck rails, eaves, and porch ceilings are favorite targets.
Beyond the holes themselves, carpenter bees leave yellowish-brown staining around tunnel entrances from their fecal matter. Over multiple seasons, repeated drilling in the same area can riddle a board with tunnels and weaken it significantly. The staining and perfectly round holes on exterior wood surfaces are usually enough to identify the culprit without any further investigation.
How to Tell Frass Types Apart
When you find a mysterious pile of debris near wood, the texture and shape of the particles tell you which insect produced it:
- Drywood termite frass: Uniform, gritty pellets with six concave sides, each about 0.5 to 1 mm long. Feels like coarse sand or coffee grounds. Color matches the wood being consumed.
- Carpenter ant frass: Irregular, fibrous, and splintery. Contains visible wood shavings and sometimes insect parts. Feels like compressed sawdust between your fingers. No consistent pellet shape.
- Powderpost beetle frass: Extremely fine powder, either silky smooth (lyctid) or slightly gritty (anobiid). Falls out of tiny round exit holes. No visible pellets or shavings.
If you’re unsure, pick up a small amount between your fingers. The difference between the fine grit of termite pellets, the fibrous texture of carpenter ant debris, and the talc-like powder of beetle frass is easy to feel even if it’s hard to see with the naked eye.
Sounds Inside Walls
Some termite species produce audible sounds. Soldier termites bang their heads against tunnel walls to signal alarm to the colony, creating a faint clicking or tapping noise. In large infestations, the combined sound of many soldiers head-banging in rapid bursts of three to four taps can be heard through walls or wood surfaces, especially in quiet conditions. Worker termites also make a softer rustling or crunching sound as they chew, though this is much quieter and harder to detect without placing your ear directly against the wood.
Carpenter ants can also produce faint rustling sounds inside walls, particularly at night when they’re most active. If you hear consistent soft crackling from a wall cavity, especially near areas with moisture damage, it’s worth investigating further.
Where to Look First
Wood-destroying insects gravitate toward moisture. Subterranean termites need soil contact and water, so check where plumbing enters the foundation, around leaky faucets, and in crawl spaces where ventilation is poor. Carpenter ants prefer wood that’s already been softened by water damage, so bathrooms, kitchens, and areas around roof leaks are prime spots.
Drywood termites and carpenter bees are less tied to moisture. Drywood termites can infest any exposed wood and are most common in coastal and southern states. Carpenter bees prefer untreated exterior wood that faces south or gets full sun. For powderpost beetles, focus on hardwood flooring, furniture, and any wood that was stored improperly before installation.
Tap suspect wood with the handle of a screwdriver. Solid wood produces a sharp, ringing sound. Damaged wood sounds hollow or dull, and in advanced cases, the screwdriver handle may punch right through the surface into empty galleries behind it.