What Woodworm Damage Looks Like in Floors, Lofts and Furniture

A 60‑second visual definition: what “woodworm damage” actually looks like (and why holes aren’t the whole story)

Woodworm damage usually shows up as small round exit holes, pale wood dust and timber that feels weaker than it looks when you press or tap it. In UK homes “woodworm” almost always means beetle larvae tunnelling inside floorboards, joists, roof timbers or furniture, while you only see the adults’ exit holes, the frass they push out and any hollowness under the surface. That is why you always read holes, dust and timber condition together, not in isolation.

Small clues on the surface often add up to a much bigger story in the timber.

What those little holes actually are

Those neat, round holes are not where woodworm starts; they are the emergence holes where adult beetles have chewed their way out after feeding inside for years. On softwood floors and roof timbers, common furniture beetle usually leaves pin‑sized holes one to two millimetres wide, while larger round holes in damp or previously decayed hardwood can point to beetles such as deathwatch. Patterns matter as much as size, because dense “peppering” in the paler sapwood and far fewer holes in darker heartwood strongly suggest beetle activity rather than random damage.

Why holes on their own don’t prove it’s active

Exit holes are scars, not proof of live activity. Once a beetle has bored its way out, the hole can remain visible for decades. If boards are sanded, paint is stripped or carpet is lifted, very old holes can suddenly look “new” simply because they have been re‑exposed.

That is why professionals treat holes as one part of a bigger picture. Fresh activity is about change over time: new holes appearing, powder re‑appearing after cleaning, or timber that feels weaker than it should. If you only glance once and see holes, you cannot reliably say whether anything is still happening inside the wood.

Frass: the “woodworm dust” that tells you more

Frass is the mixture of chewed wood and droppings the larvae push out of their tunnels. In practice it shows up as:

• Fine, pale, talc‑like dust or slightly gritty pellets.
• Little heaps directly under or beside exit holes, on ledges, in floorboard gaps, on top of plaster or insulation.

Fresh frass tends to look clean and light in colour, and it falls easily when the timber is tapped or moved. Old frass can be compacted, darkened or stuck to surfaces. The key question is not “Is there dust?” but “Does it come back after you have cleaned it?”

Why context – floor, loft or furniture – matters

The same beetle can leave very different‑looking evidence on a loft rafter, a ground‑floor board or a waxed chest of drawers. On floors, dust may be trapped in gaps and along skirtings. In lofts, it can fall onto insulation or ceiling plaster. On furniture, it hides under feet, inside joints and in the bottom of drawers.

Before you try to decide what anything means, pause and note three things: the type of timber, the location (floor, loft, furniture) and how easy it is for dust to fall and collect there. That simple habit makes every later check more useful and stops you chasing the wrong clues.

A specialist such as Sussex Damp Experts will start with exactly these basics, then build up a picture from multiple clues rather than reacting to holes in isolation.

The visual checklist people mean by “woodworm”: holes, frass, weakened timber, surface changes and beetles

A simple visual checklist helps you spot woodworm damage reliably by forcing you to read several clues together instead of reacting to one feature. You look at the shape and size of holes, the type and position of dust, how the timber feels, any changes to the surface finish, and – occasionally – the insects themselves. Surveyors and timber specialists use the same sequence on inspections because it stops you jumping to conclusions from a single clue, and thinking in terms of this checklist also stops you over‑reacting to one feature and helps you describe what you are seeing clearly if you later ask for help.

Exit holes: size, shape and pattern

Exit holes act like a map of beetle activity: their size, shape and distribution show where larvae have been feeding and how serious the attack might be. Tiny, pencil‑tip holes scattered across softwood often suggest light, general activity, while larger round holes grouped in damp‑damaged hardwood can signal higher risk. Lines, bands or clusters along edges, ends and damp junctions usually matter more than a few isolated holes in otherwise solid timber.

Look at:

• Diameter – tiny or clearly larger than a pin.
• Shape – round and clean, or ragged, or more oval.
• Distribution – scattered, clustered “shotgun” patches, or bands along edges and end grain.

Patterns that line up with damp, sapwood bands, ends of beams or junctions with masonry are much more significant than a few random holes on an otherwise sound piece of timber.

Hole edges: fresh rims vs old scars

Now look closely at the edges of the holes.

Fresh or recent emergence often shows as sharp, crisp rims with bright, pale wood visible in the hole. It can look as if the hole was drilled yesterday. Over time, light and air darken the cut surface, dust dulls the edges, and paint or varnish can partly fill or soften the outline. On walked‑on floors and handled furniture, wear and cleaning blur and round those rims.

This “rim test” is useful but not foolproof. Sanding, stripping or aggressive cleaning can make very old holes look sharp again, and grime can make relatively recent holes look older than they are. Treat edge appearance as one clue among several, not a verdict on its own.

Frass: gritty pellets or fine powder

Frass is often the most helpful indicator once you know what to look for, because it behaves differently from normal household dust. With many common house beetles, frass feels gritty between your fingers and under magnification looks like tiny pellets or crumbs; with others it is much finer, more like flour or talc. Either way, what matters most is that it appears directly beneath or beside exit holes and returns in the same place after you have carefully cleaned it away.

You do not need to handle it much. A gentle tap on the timber and a look at what falls onto a piece of contrasting paper beneath is usually enough.

Weakened or “shell” timber

Internally, larvae can turn sound wood into a honeycomb of tunnels while leaving a thin outer “skin”. From the outside the piece may look acceptable, yet:

• It sounds hollow or papery when tapped compared with adjacent timber.
• Edges or arrises crumble easily when lightly pressed.
• Fixings around it begin to loosen for no obvious reason.
• Slight deflection or “bounce” appears in floors.

Take care not to gouge or lever at suspected areas; the aim is to notice abnormal softness or hollowness, not to create new damage.

Surface changes and finish disturbance

On painted, stained or polished surfaces, woodworm damage can show as:

• Tiny craters or pin‑holes that break an otherwise even finish.
• Small blisters, ripples or fine cracks radiating from a cluster of holes.
• Patches where sheen, colour or grain look subtly different, suggesting filler or a repair.

On furniture and joinery you may also see “over‑finished” spots where a local repair has been disguised under a heavier coat of polish or stain.

Occasionally, the insects themselves

It is relatively rare to see live beetles or larvae, but if you do, that is important evidence. Adult beetles emerging in late spring or summer may be found on window sills or near light sources, or caught in spider webs close to affected timber. Larvae are usually hidden inside the wood.

If you capture an insect, keep it in a small ventilated container and photograph it against a scale rather than trying to identify it by guesswork. Combining the insect with the hole and frass evidence gives a much stronger picture of what is going on.

Active vs historic: the clean–mark–catch–re‑check method (so you can stop guessing)

Active woodworm shows itself through repeatable change over time, not just by a single snapshot of holes and dust. To tell the difference between live activity and old scars, you clean the area, mark what you are watching, set up a way to catch any new frass, then re‑check on a simple schedule. This “clean–mark–catch–re‑check” method turns guesswork into evidence you can show to a surveyor or timber specialist.

Good notes turn a vague worry into something you can act on calmly.

Step 1 – Clean: reset the evidence

Cleaning is about resetting the evidence so anything that appears afterwards is genuinely new and worth noting. Gently remove loose dust and debris around the suspect area with a vacuum and soft brush, or a dry brush and pan, taking care not to scour delicate surfaces or drive powder deeper into cracks. Once the area is as clean and dry as practical, any fresh frass you later see has a clear starting point in your notes. Avoid wet cleaning near bare timber, because moisture can blur evidence and affect the wood itself.

Step 2 – Mark: fix locations in your memory (and photos)

Next you mark what you are watching.

Take clear photos showing the pattern of holes, ideally with a ruler, tape or coin in shot for scale. Make a simple sketch plan noting where the timber sits in the building – for example, “front left bedroom, board two from wall, near radiator” or “loft, third rafter from hatch on party wall side”.

You can also put a small pencil dot or piece of low‑tack tape beside a representative cluster. This helps you compare “before” and “after” later on.

Step 3 – Catch: let gravity help you

Then you set up something to catch any new frass that falls.

Slip a sheet of plain, contrasting paper, a shallow tray or a card strip directly under the suspect face: beneath floorboard gaps, under the edge of a beam, or on top of a clear patch of loft insulation. The point is to position it so that any fresh frass has a clean, undisturbed surface to land on.

Label the catcher with the date so you can track how long it has been in place.

Step 4 – Re‑check: look for repeatable change

Finally you re‑check on a sensible schedule – perhaps after a week, then again after a month, and once more the following season.

You are looking for:

• New dust on your catching surface that lines up with holes above.
• New dust appearing again after you remove it.
• Any new holes that were not there in your original photos.
• Changes in how the timber feels or behaves, such as more give in a floorboard.

One‑off dust that never returns, especially after building work or cleaning, is much less concerning than fresh frass that keeps appearing under the same spot.

Recognising false positives

Once you have run a cycle or two, it becomes easy to misread disturbed old dust as new activity if you are not careful. Plenty of everyday activities can move old debris into new places:

• Sanding floors or beams.
• Drilling, chasing or rewiring.
• Loft insulation being dragged or pushed around.
• Pets, children or general traffic disturbing old debris.

If your catcher picks up a jumble of different materials – plaster crumbs, insulation fibres, grit – think “disturbance” first. Then go back to your photos and ask whether holes or patterns have actually changed.

When your notes say “time to escalate”

If, after a couple of rounds, you see new frass in the same place, perhaps along with new holes or softening timber, it is reasonable to treat the infestation as potentially active and get a closer look. At that point your logs and photos become very helpful because they show:

• Where in the building to concentrate on.
• How long the signs have been appearing.
• What else has been happening nearby, such as leaks, condensation or building work.

A timber specialist, surveyor or a firm such as Sussex Damp Experts can then add moisture readings, construction knowledge and, where justified, selective opening‑up and timed re‑inspections. Together these turn your observations into a firm diagnosis before anyone goes ahead with treatment or repair.

Floors and subfloors: what woodworm damage looks like where you walk (boards, joists, skirtings, voids)

Floors with woodworm often show a mix of surface clues and hidden changes below the boards, and you only get the full picture when you read them together. Exit holes and frass at gaps and skirtings, softened or “bouncy” areas, and heavier damage on the hidden underside of boards and joists all matter. Surveyors often find that subfloor evidence tells a different story from the room surface, especially where damp and ventilation have been uneven over time.

Because subfloors trap dust and are influenced by moisture and airflow, floor evidence often looks different from what you see in a loft or on furniture.

Surface signs on boards and skirtings

Surface signs on floors usually start subtle and localised, so you need to slow down to see them. Small round holes along board edges, fine pale dust in gaps, and speckling near skirtings or pipe penetrations are typical. You tend to notice more around old carpet lines, under furniture and close to damp external walls, where timber has stayed cooler and slightly wetter. Taken together, these patterns tell you where to focus any closer checks or subfloor investigation.

Typical surface clues include:

• Small round holes across exposed boards, particularly along edges or in old, previously carpeted areas.
• Slight “peppering” along the softer outer band of boards, especially towards walls.
• Fine, pale dust in gaps between boards, along skirtings or around radiator pipes and other penetrations.

Sometimes boards look visually fine, but skirtings or the bottoms of door frames show holes and dust where timber is closer to damp masonry. Because floors are walked on and cleaned, dust can be disturbed quickly, so you may need to look closely at protected corners and under furniture.

What happens on the underside

Underneath, things can look quite different from the neat floor surface you see from the room.

The underside of boards may show far more exit holes than the top, because beetles emerge into the cooler void rather than up into a heated room. Joists can show localised clusters near damp walls, at bearing points on sleeper walls or where ventilation is poor. You may also see cobwebs with caught frass or beetle bodies beneath heavily attacked areas, which is a strong clue that activity has been focused there rather than across the whole floor.

If you have safe access via a cellar hatch or removable panel, a torch‑lit inspection can be revealing. You are checking for heavier peppering on the underside of suspect boards, zones of more intense activity where joists meet walls, and frass piled on ledges, pipes or cables below. If anything about access feels unsafe or unclear, it is better to stop and bring in someone competent than risk damaging the structure or yourself.

Floors that feel different underfoot

Changes in how floors behave can be as important as visual signs.

Timber that has been heavily tunnelled can leave a thin crust above a void. Signs include:

• Localised “springy” patches compared with the rest of the room.
• Noises or slight movement around particular boards when you walk.
• Crumbling edges where boards meet thresholds, stairs or exposed corners.

In a typical 1930s semi, for example, you might feel a slight bounce by the bay window, hear a creak in one board and see a line of dust where the skirting meets the floor. That sort of pattern is enough to justify a closer look at the underside rather than assuming it is just age or poor workmanship.

These changes do not automatically mean failure is imminent, but they are a clear signal that the structure needs a proper assessment, particularly if combined with fresh frass or new holes.

The role of moisture and subfloor ventilation

Subfloor voids are easily overlooked but strongly influence beetle activity and long‑term timber health.

Blocked air bricks, high external ground levels, leaking pipes or damp soil under suspended floors can all increase timber moisture. Over time that makes conditions more attractive to wood‑boring insects and can promote decay as well, especially where timbers bear into damp masonry or sit above wet ground.

Visually, you might see darker staining on joists or the underside of boards near walls, efflorescence or damp signs on adjacent masonry, and signs of mould or a generally musty smell in the void. If you connect these moisture clues with woodworm evidence, your plan needs to tackle both: the insects and the conditions that support them.

A thorough survey will normally include moisture readings and a check on ventilation and external ground levels as well as visual timber inspection.

Knowing when to stop lifting boards

It is tempting to pull boards up to “take a quick look”, but that can introduce its own problems: damage to tongues and grooves, plaster cracking, disturbed services and difficulty refitting floors neatly.

If you do not already know what is under your floor – for example, where pipes, cables, heating or insulation run – it is usually better to pause once you have confirmed that visual evidence exists on accessible faces. Bringing in someone competent who can open up safely and selectively often results in a clearer diagnosis and tidier repairs.

Lofts and roof timbers: what you’ll see on rafters, purlins, joists and sarking (and what insulation can hide)

In lofts and roof spaces, woodworm damage usually shows up where beetles can feed on softer, damper timber and where dust can fall onto insulation or plaster below. Sapwood edges, damp‑affected rafters, purlins (horizontal beams supporting rafters) and ceiling joists carry most of the risk, and the insulation or plaster often catches the frass that trickles down. Because roof spaces are cooler, more varied in moisture and often part‑concealed by insulation, the patterns you see there can be quite different from those on a living‑room floor.

Roof‑space hotspots and “peppering” along edges

Certain roof timbers are much more likely to show woodworm than others.

Beetles favour sapwood edges, waney‑edged rafters with traces of bark, and damp‑affected rafters, purlins and ceiling joists near past leaks or condensation. On these pieces you often see bands of tiny round holes following the pale sapwood strip, clusters around nail holes and slight surface rippling where frass and tunnelling sit just below the surface.

By contrast, dry, well‑ventilated timbers away from damp masonry or roofing defects may show no visible signs at all, even in the same roof.

Dust on insulation and plaster below

In many lofts the clearest evidence appears on surfaces below the affected timbers rather than on them.

Frass often trickles down onto:

• The top surface of quilt insulation.
• The back of ceiling plasterboard.
• Horizontal surfaces such as binders, bracing or the top of internal walls.

You may see faint lines or little piles of dust that seem to form beneath a particular rafter or junction. If the timber face itself is buried under insulation or inaccessible, these “drop lines” help you trace where activity is likely. In one roof, for example, you might find a pale dust stripe running across insulation directly under a rafter that once leaked, while the bays either side stay clean. That contrast is a strong clue about where to concentrate checks.

It is important not to confuse old building dust with frass. Old plaster crumb, debris from previous work and insulation fibres can all look similar at first glance. As with floors, cleaning and re‑checking is the safest way to see what is genuinely new.

Seasonality and re‑checks

Lofts respond strongly to the seasons.

Adult beetles tend to emerge in the warmer months. If you notice dust or new holes at that time, it is sensible to do a clean‑and‑re‑check cycle over the following weeks and months. In cooler seasons, fresh emergence is less likely but not impossible, especially in heated loft conversions or spaces with high background moisture.

You do not need to be up there constantly. A couple of planned inspections spaced across the year, with photos and brief notes, can give you a much clearer picture than a single hurried look when you happen to fetch the decorations.

Distinguishing insect damage from decay

Roof timbers are also prone to fungal decay where they have stayed damp.

Decay usually presents slightly differently to insect damage, although the two can exist together:

• Wood feels soft, fibrous or spongy rather than hollow and crisp.
• Surfaces show characteristic cracking patterns or cuboid “checking”.
• There may be obvious staining, tide marks or historic leak evidence.

If you see these signs without exit holes or frass, the primary problem may be moisture and decay, with or without beetle involvement. Either way, the condition of the roof and its drainage and ventilation will need attention in any long‑term plan.

Respecting access and safety limits

Loft inspections are easy to do badly and hard to do well if access is poor.

Thin plasterboard, unboarded joists, electrical cables, fragile insulation and stored items all increase the risk of a misstep or damage. It is perfectly reasonable to limit yourself to what you can safely reach from solid boarding or a safe working platform, then record which areas you could not see.

When a specialist timber surveyor inspects a roof space, they will weigh up this access and safety picture before deciding how far to go. They will measure moisture levels where appropriate and state clearly in a report which parts of the structure were and were not inspected.

Furniture and antiques: what woodworm damage looks like on finished, repaired, veneered and upholstered pieces

On furniture and antiques, woodworm damage reveals itself on hidden faces, in sheltered corners and in the way finishes behave, rather than on the most polished show surfaces. You get the best information from undersides, backs, joints and runners, then from tiny changes in varnish, wax or stain. Conservators and specialist restorers rely on these hidden faces and finishes when they assess valuable pieces, and they separate genuine insect damage from normal ageing so fragile items are not exposed to unnecessary treatment.

Where to look first on a piece of furniture

The safest way to read furniture is to start on the hidden faces that everyday use and cleaning rarely disturb. Tilt or carefully lift the piece so you can see undersides of feet and stretchers, the backs of cabinets, drawer sides and runners, and the underside of chair seats near upholstery edges. These sheltered areas are where fresh frass and exit holes tend to remain undisturbed and easiest to judge.

Turn or tilt items safely to inspect:

• The underside of feet, stretchers and rails.
• The backs of cabinets, wardrobes and chests.
• Drawer sides, runners and the insides of carcasses.
• The underside of chair seats, especially under upholstery edges.

You are looking for small round holes, frass sitting in sheltered corners and any sign of “peppering” along softer sections of the wood. A chest of drawers may look perfect on the front, yet when you pull the bottom drawer out you find frass sprinkled on the runners and small holes on the unseen back panel, which tells you far more than a quick glance at the polished faces.

How finishes and polish can hide or reveal damage

On finished surfaces, woodworm damage and repairs often show up in the way light reflects.

Clues include:

• Tiny dull spots or craters breaking a glossy varnish or lacquer.
• Micro‑cracks or slight ridges radiating from a cluster of holes.
• Patches where the sheen or colour is subtly different, suggesting filler or over‑polishing.

Heavy wax or stain can be used to disguise holes, leaving slight domes of finish where the material has bridged a small void. Under raking light from a torch, these tricks often stand out clearly even when the piece seems fine in normal room lighting.

Repairs, replacements and concealed galleries

A repaired antique can legitimately have had insect damage removed and sound timber spliced in. Problems arise when only the outward signs are treated and internal galleries remain nearby, so fresh activity can continue unnoticed behind a neat repair.

You may see:

• New sections of timber let into old work, with join lines running across grain.
• Patches of veneer that do not quite match, especially on less visible areas.
• Filler plugs where clustered holes once were, now sanded and stained.

These are not automatically bad – they may be part of a responsible restoration – but they remind you that internal condition matters as much as what the eye can see. Fresh frass in or around repaired zones is a strong reason to pause and seek a specialist opinion before buying, selling or treating.

Sensible quarantine without panic

If you suspect an item might be shedding active frass, it is reasonable to isolate it from vulnerable structural timber while you gather evidence.

In practice that means:

• Moving it away from direct contact with skirtings, joists or exposed structural beams.
• Placing it in a clean, accessible spot where you can see any fresh dust that appears.
• Laying paper or card beneath key areas to catch debris between checks.

Avoid over‑reacting by dragging fragile pieces over rough floors or exposing them to sudden changes in temperature or humidity just to “get them out of the way”. Containment is about observation and control, not punishment.

Don’t miscall it: woodworm lookalikes and the “when to worry” threshold for structure, sales and safety

Clear thresholds stop you over‑ or under‑reacting to woodworm signs by tying your concern to repeatable evidence and real‑world impact. You avoid miscalling woodworm by knowing its common lookalikes and by asking whether the signs could affect strength, safety or a sale, rather than reacting to every mark. Surveyors and lenders routinely separate cosmetic scars from structural or transactional risk in exactly this way, so they neither ignore genuine problems nor treat harmless features.

Common hole and dust lookalikes

Many suspicious‑looking holes and dust patches turn out to be something other than woodworm. Old nail, screw or staple fixings, small manufacturing defects, open grain and former fitting points for hinges or upholstery can all mimic exit holes, especially when viewed in isolation. Likewise, plaster, brick, mortar and insulation dust, or just long‑settled household dust from simple neglect, can gather on or below timber, spread more widely and feel different to beetle frass, which tends to sit tight beneath a focused cluster of holes.

Several everyday features can mimic exit holes:

• Old nail, screw or staple holes, especially in lines or regular patterns.
• Manufacturing defects such as tiny tear‑outs, knot “pips” or open pores in certain hardwoods.
• Former fitting points for upholstery, hinges or shelf supports.

Similarly, dust from plaster, brick, mortar, insulation or simple neglect can gather on or below timber and look suspicious at first glance. These materials often feel different between the fingers and may be spread more widely, not just beneath a tight group of holes.

The questions to keep asking are: “Does the pattern of holes make sense for insects?” and “Does dust re‑appear in the same place after careful cleaning?”

When species clues start to matter

Hole size, frass type and timber preference do matter, but only once you have the basics in place.

Larger, round holes in damp, previously decayed hardwood, for example, are more worrying than tiny holes in dry, well‑ventilated softwood with no fresh dust. Oval or ragged holes in certain roof timbers, combined with distinctive frass and severe internal loss, can indicate beetles that carry higher structural risk.

Rather than trying to become an entomologist overnight, use species clues as a way to rank concern: “low, medium, high” based on a bundle of signs, not just one measurement.

The point at which woodworm stops being a cosmetic issue and becomes a structural or transactional concern is when evidence stacks up in both columns.

For structure, worry increases when you see:

• Fresh frass or new holes in load‑bearing members.
• Obvious reduction in cross‑section, such as edges crumbling or hollowness.
• Movement, cracking or deflection linked to affected timbers.

For sales and safety, risk increases when:

• A survey flags widespread damage without a clear statement on activity.
• There is uncertainty over what is under floors or behind finishes.
• Multiple parties, such as buyer, lender, insurer, landlord or tenant, will rely on the findings.

At that point a written, evidence‑based opinion from a competent timber specialist matters as much as what you can see yourself.

Keeping moisture and treatment in the right order

Because wood‑boring beetles are strongly influenced by timber moisture, many serious cases are as much a damp problem as an insect problem.

If someone proposes chemical treatment, it is reasonable to ask:

• What is the condition of the timber and adjacent masonry?
• How are ventilation and moisture being addressed?
• Will any repairs be needed to restore lost section?

Addressing moisture and beetles together makes recurrence far less likely and protects the value of any repairs you go on to commission. It also lines up with the way most good property surveys treat damp and timber issues, by looking at causes and effects together rather than in isolation.

Book Your Consultation With Sussex Damp Experts Today

Sussex Damp Experts help you turn scattered signs of woodworm into a clear yes‑or‑no view on activity, plus a practical plan for what to do next. A consultation should leave you with a plain‑language opinion on whether the signs look historic, active or uncertain, what moisture and ventilation are doing, which parts of the structure, if any, need closer investigation, and a written record you can share with surveyors, buyers, lenders, tenants or insurers, plus a prioritised set of options rather than a single take‑it‑or‑leave‑it quote.

On a visit, our surveyor follows the same evidence‑led approach you have been using: reading holes, frass and timber condition, taking moisture readings, and, where it is sensible, using low‑disturbance methods such as selective lifting of one or two boards or safe hatch access in lofts. We also work to keep disruption to a minimum and to respect existing finishes and structures while still gathering the evidence needed for a firm opinion.

Afterwards you should have a clear next step rather than an open‑ended worry. If repeat frass, new holes or changing floor or roof behaviour are starting to concern you, this is the moment to act rather than keep wondering. Book a consultation and turn scattered clues into a clear, evidence‑based plan.

Frequently Asked Questions