Rotten Before It Looks It: Wood Decay Fungi, the Twenty Per Cent Threshold, and the Carpenter Ant as Symptom

1. Introduction: the agent nobody calls about

A pest control company in this climate is called about carpenter ants many times each season. It is almost never called about the fungus that made the wood habitable for them.

This is an inversion of structural importance. The fungus removes the strength of the timber. The ant removes some of the timber, usually after the fungus has already ruined it, and in a volume that rarely exceeds a few square feet.¹¹

1.1 Scope

This paper covers decay fungi in structural timber, the moisture conditions that permit them, the timing of strength loss, and the relationship to Camponotus. It does not cover mould, which is a surface growth with different organisms, different health implications and a different literature.

2. The twenty per cent rule

The single number that governs this entire subject.

Industry guidance states plainly that fungal decay always arises because the wood has become wet, in excess of 20 per cent moisture content, and that finding the source of dampness and eliminating the ingress of moisture, whilst promoting drying, is always necessary.⁸

2.1 Why a single threshold is useful

Most of this journal has concerned organisms whose control depends on many interacting variables. Decay fungi are unusual in having one dominant variable that is measurable with an inexpensive instrument.

A moisture meter reading below the threshold means decay is not progressing. That is a stronger diagnostic statement than anything available for bed bugs, cockroaches or rodents.

2.2 The corollary

If moisture is necessary, then a building that stays dry does not rot, regardless of what spores land on it. Timber in a dry wall cavity is not at risk, and treating it achieves nothing that drying it would not.

3. The thresholds in detail

The research literature is more granular than the 20 per cent figure, and the granularity matters.

Using a technique that measures wood moisture in flasks containing piled sapwood samples, Huckfeldt and colleagues reported for Serpula lacrymans a 21 per cent minimum moisture content for sample colonisation and 26.2 per cent for wood degradation.¹

Other reported values include a minimum of 30 per cent for Coniophora puteana on Norway spruce, and a range between 40 and 70 per cent moisture content for optimal action of the basidiomycetes.¹

3.1 The colonisation and degradation gap

The gap between 21 and 26.2 per cent is worth dwelling on. A fungus can establish itself in timber at a moisture content below the level at which it can damage it.

That means a building can hold a dormant colonisation that becomes active later if conditions worsen, which is a different situation from a building with no fungus present at all. A reading taken during a dry period does not establish that nothing is there.

3.2 Below fibre saturation

Some work has shown degradation below the fibre saturation range, though at relative humidity values above 96 per cent, and other work reported degradation below fibre saturation on wood with an initial moisture content above 19 per cent.¹

The practical reading is that thresholds are not sharp edges. They are approximate boundaries that vary by fungal species, wood species and the history of the sample.

4. Initiation against maintenance

A distinction with direct remedial consequences.

Serpula lacrymans and Meruliporia incrassata require an elevated moisture content to initiate an attack on timber, of 28 to 30 per cent. Once established, the fungi can remain active in timber with a moisture content of more than 20 per cent.²

4.1 The ratchet this creates

The condition required to start is more demanding than the condition required to continue. A single wetting event above 28 per cent can establish an infection that then persists at a moisture level the building routinely reaches.

So remediation cannot aim at the initiation threshold. It has to bring the timber below the maintenance threshold, which is the lower and more demanding target.

4.2 Fruiting

A moisture content of 30 to 40 per cent is described as the ideal level in wood to promote fruit body formation.⁶

Visible fruiting bodies therefore indicate conditions substantially wetter than those needed for the decay itself, which is why their absence is not reassurance.

5. Humidity and equilibrium moisture

Wood moisture is set by the air around it, so the thresholds can be restated in terms of humidity.

At relative humidities below 86 per cent, growth of S. lacrymans is inhibited, but it can stay dormant at relative humidities down to 76 per cent. These correspond to equilibrium moisture contents of wood of 19 and 15 per cent respectively.²

5.1 What dormancy means for remediation

A fungus that survives dormant at conditions well below those it needs to grow is one that a temporary drying will not eliminate.

This is the same pattern as the protected life stages examined elsewhere in this journal. The flea cocoon, the cockroach ootheca, the spider egg sac and a dormant mycelium all persist through conditions that kill the active organism, and in each case the answer is to change the environment rather than to wait out the treatment.

6. What brown rot actually does

The mechanism explains everything that follows about detection.

Brown-rot fungi depolymerise cellulose rapidly during incipient stages of wood colonisation. Cell wall carbohydrates are degraded extensively during decay, leaving a modified, lignin-rich substrate. The residual wood is brown and often cracks into cubical pieces when dry.⁵

The enzymatic account is more specific still. Early tensile strength loss occurs in wood that may still appear intact because the enzymes can extract sugars from cellulose without at first disturbing the lignin framework of the wood cells. Genomic analysis has shown a highly evolved system of scores of cellulose-digesting enzymes synthesised whenever the hyphae meet a wood food source.⁷

6.1 The structural reading

Cellulose provides tensile strength. Lignin provides rigidity and the visible structure. A fungus that removes the first while leaving the second produces timber that looks like timber and performs like something considerably weaker.

As cellulose is progressively removed, the wood becomes brown, breaks up by transverse and horizontal cracks into cubes, and eventually collapses into a dry brown powdery lignin residue.⁷ By that point the diagnosis is trivial and the timber is gone.

7. Strength before symptom

The finding that should govern inspection practice.

Considerable losses in wood strength occur very early in the decay process, often before decay characteristics are visually evident.⁵

7.1 The numbers attached to that

In the description of early or incipient decay, strength loss varies widely depending on fungal species and wood type, with reductions of 6 per cent to 50 per cent when mass is depleted by 1 per cent to 10 per cent.³

A timber can therefore have lost half its strength having lost a tenth of its mass, at a stage where dimensional changes are minimal.³

7.2 Why visual inspection fails here

Visual inspection detects mass loss and dimensional change. The strength loss arrives first and the mass loss arrives later, so the inspection method is measuring the lagging indicator.

This is not a criticism of inspectors. It is a property of the organism, and it means that a timber passing visual inspection has not been shown to be sound.

8. The strength to mass ratio

Several studies have quantified the relationship, and the ratios are consistent in direction if not in magnitude.

Biodeterioration by Serpula lacrymans has been reported to produce a mass loss of 6 per cent at 12 weeks together with a decrease in parallel compression strength of 33 per cent.⁴

For Coniophora puteana on wild pine, a compression strength loss of 50 per cent was obtained for a mass loss of 20 per cent. For southern yellow pine exposed to Gloeophyllum trabeum for 72 days, a relationship between strength loss and mass loss of four to one was established.⁴

8.1 The consistent finding

Across three fungi and three timber types, strength falls several times faster than mass. The four to one figure is the cleanest statement of it.

8.2 The caution the authors give

The study reporting these comparisons noted that no linear relationship was observed across the various periods evaluated, and that its most significant relationship was obtained with the incipient attack at 30 days.⁴

So the ratio is not a constant that can be applied to convert one measure into the other. What it supports is the directional claim, which is that mass loss understates damage, and most severely in the early period when intervention would matter most.

9. What early decay looks like

Since the damage precedes the obvious signs, the subtle signs are worth listing.

Researchers with the United States Department of Agriculture Forest Products Laboratory describe three to five progressive stages of wood decay under varied and localised conditions. Early or incipient stages are characterised by slight to moderate discoloration, such as bleaching or darkening of the grain, sometimes imparting a blotched or mottled appearance. The surface may exhibit a sheen and appear persistently wet with the advancement of the mycelium. Dimensional changes are minimal.³

9.1 The operational point

Persistent wetness with a sheen, and mottled discoloration without dimensional change, are the observable stage at which action is still cheap.

These are also exactly the observations a technician makes routinely while inspecting a basement or crawlspace for insects, and they are commonly not recorded because they are not what the visit was about.

10. Dry rot as an organism

The species with the worst reputation deserves a plain description, because the reputation interferes with the diagnosis.

Serpula lacrymans is considered the most aggressive and harmful brown-rot fungus for wooden buildings worldwide and has led to substantial economic losses.⁴ It is well known for destroying timbers in buildings and spreading from floor to floor through hidden spaces, and its appearances throughout an affected building have led to a sometimes almost mystical fear of its destructive abilities.⁷

10.1 The deflation

The corrective from the same source is worth quoting for its tone. It is only a woodland fungus that happens to have developed a capacity to grow in buildings. Its ancestral habitat is cool pine forests, where it feeds on fallen dead wood on the moist forest floor.⁷

A building containing softwood embedded in damp masonry provides all the conditions to which the fungus has become adapted by natural selection in its original forest home: damp softwood to feed on, a moist surface from which it can scavenge mineral nutrients, and damp enclosed spaces to grow in.⁷

10.2 Why that framing helps

An organism described as a plague invites drastic and expensive response. An organism described as a forest fungus finding a forest-like habitat invites the question of which building condition is providing it, which is the question that leads to the fix.

It is also worth noting that it affects softwood,⁷ which is what Canadian light-frame construction is made of.

11. Scavenging minerals from masonry

An unusual capability that explains part of the building association.

The fungus appears to require an environment where both inorganic and organic materials are present, and uses calcium and iron ions extracted from plaster, brick and stone to aid the breakdown of wood.⁶

11.1 The consequence for where it appears

Painted surfaces of timber such as skirting boards are usually colonised by mycelium growing through damp underlying masonry.⁷

So the fungus arrives at the wood through the wall rather than across the room. A sealed or painted timber surface is not protected, because the colonisation does not come from the exposed face.

11.2 The inspection implication

We would draw the conclusion, as our inference, that a timber-to-masonry interface in a damp basement is the highest-yield place to put a moisture meter, and that finish condition on the visible face tells an inspector very little about what is happening behind it.

12. Surviving a discontinuous supply

The trait proposed as the reason this species is a building problem when its relatives are not.

A problem in controlling building dry rot is that we do not know what the determinants of its destructiveness are, meaning what makes it more damaging to buildings than close relatives and other wood decay fungi that inhabit forests. Its ability to infect and colonise timber in buildings has long been linked to a capacity to survive and flourish in a spatially discontinuous moisture and nutrient supply, an adaptation probably honed during evolution from ancestors in temperate and boreal regions.⁹

12.1 Why a building is discontinuous

A forest floor is uniformly damp. A building is a patchwork of wet and dry, with timber separated by masonry, voids and air gaps.

An organism that can bridge dry gaps to reach the next wet resource is suited to that patchwork in a way that a forest fungus adapted to uniform moisture is not.

12.2 The mechanism of bridging

Mycelium spreads over the timber surface by continued growth and branching of hyphal threads, and thicker strands develop within the mycelium which supply water and nutrients to the growing front as the fungus becomes established.⁸

That is the physical basis for the reputation: the organism can carry its own water forward, so the wood it colonises next need not have been wet before it arrived.

13. Why it moves through a building

Putting sections 11 and 12 together produces the behaviour that alarms people.

The fungus spreads from floor to floor through hidden spaces.⁷ It draws minerals from masonry⁶ and transports water and nutrients forward along thick strands to a growing front.⁸

13.1 What this means for the extent of works

The visible outbreak is a growing front, not the whole organism. That is why remediation of dry rot has historically involved opening up well beyond the damage, and why the extent of works is frequently disputed.

We would note that this journal has no basis for adjudicating how far that opening up should extend, and that the commercial interest of the firm doing the opening runs in one direction.

14. Wet rot and the other species

Dry rot dominates the literature and is not the common case.

A variety of wood-destroying fungi attack timber because of excess moisture. The best known are true dry rot, Serpula lacrymans; cellar fungus, Coniophora puteana; and pore or mine fungus, Fibroporia vaillantii, with many other species affecting exposed or internal timbers, some particularly linked with decay in joinery, door and window frames.⁸

Wet rot occurs more frequently but is less serious. Decay is typically confined to the area where the timber has become wet.⁸

14.1 The practical difference

Confinement to the wet area is the whole distinction. Wet rot is a local problem that ends where the water ends, which makes it tractable: fix the leak, replace the affected timber, and the matter is closed.

Dry rot is the one that travels, and it is the reason the two are worth distinguishing before deciding the scale of a repair.

14.2 Identification

Where fruiting bodies are absent, S. lacrymans can be identified by visual inspection and if necessary analysis of decayed wood.⁷ The mycelium develops extensively on infected timber and in still humid conditions produces a mass of cotton wool-like growth with bright lemon-yellow patches, with water droplets on the surface giving the species its name. Lilac tinges are more common in less humid situations, where the surface mycelium is reduced to a thin silken grey skin.⁸

15. The carpenter ant connection

The point at which this becomes a pest control subject.

Carpenter ants nest in wood structures and prefer moist wood affected by fungal decay. However, they will also nest in sound wood and in non-wood construction materials including foam and fibreglass insulation, drywall and particleboard.¹⁰

Damp or rotting wood is especially attractive for nests because they feed on fungal growth and the softer fibres make tunnelling easier.¹¹

15.1 The desiccation constraint

Unlike termites they do not digest wood, but use it as a nesting site providing a habitat that can be kept moist, since the immature stages are subject to desiccation.¹²

Moisture is essential for their activity in wood, and although they attack wood that is already moist and has begun to decay, they also supply moisture as needed by transporting it from the soil through tunnels.¹²

15.2 The ecological role

In their natural environment carpenter ants nest in dead trees and other dead wood, which enhances decay and has ecological benefits.¹³ The great majority of Camponotus species are not pests and are highly beneficial, helping to recycle decaying wood and preying on forest pests.¹⁰

15.3 What is exceptional about them

Most ant species lack the ability to excavate sound wood and instead occupy preformed cavities made by wood-boring beetles or termites; Camponotus is the exception. As wood becomes more decayed and soft, species other than Camponotus may also become able to excavate it.¹⁴

16. What the ant is telling you

The diagnostic content of an indoor carpenter ant colony.

Its existence inside a structure is usually most important as a sign that there is or has been a water problem.¹¹

16.1 The conditions that promote infestation

Reported promoting conditions include proximity to forest, wood in contact with soil, vegetation in contact with the structure, roof or gutter leaks, and infested trees on the property.¹⁰

Four of those five are moisture conditions or delivery routes for moisture, and keeping gutters clear so that water does not run down the side of the structure is named as the easiest preventive measure.¹³

16.2 The inference we draw

A carpenter ant treatment that does not include a moisture investigation has addressed the visible organism and left the condition that produced it. We would put this more strongly than the sources do: in a structure with an established indoor colony, the moisture finding is the more valuable deliverable, and it is the one the client is not paying for.

16.3 Nature of the galleries

Excavations look sandpaper smooth and are kept very clean, unlike termite galleries which are packed with mud and excrement.¹¹ Galleries run parallel to the grain, created in the softer, non-aligning portions of the timber.¹³ Wood particles are expelled from holes or slits in the surface, and sawdust piles are evidence of infestation.¹²

17. The satellite nest problem

Why locating the colony is harder than it appears, which matters because the damp nest and the dry nest are in different places.

The queen, eggs, early-instar larvae and workers are located in the parent nest, usually in a standing live or dead tree, rotting wood, or a wooden structure. Workers, mature larvae, pupae and winged reproductives are found in satellite nests, which are often excavated in drier, solid wood.¹⁰

Satellite nests can be numerous and often difficult to locate by visual observation alone, and may account for as much as 75 per cent of structural infestations.¹⁰

17.1 Why this complicates the moisture story

If three quarters of structural infestations are satellite nests in drier solid wood, then a substantial proportion of indoor carpenter ant activity is not sitting in decayed timber at all.

The parent colony outside may be in rotting wood while the indoor satellite is in sound framing. The most common route of invasion is described as a mature colony nesting outside setting up a satellite nest inside.¹⁰

17.2 The honest qualification

This weakens the clean version of the argument. The ant indoors is a reliable signal of moisture somewhere in the system, but not proof that the timber it occupies is decayed.

We would rather state that than overclaim, and note that the same source reports preference for moist or decaying wood while stating that nesting sites are not restricted to such areas.¹⁵

18. Which organism does the damage

Setting the two side by side.

Carpenter ant tunnelling may cause serious structural damage if it occurs in key timbers, but nest sites rarely exceed a few square feet.¹¹ Colonies develop relatively slowly, with 300 to 2,000 workers produced over a two year or longer period.¹⁵

Against this, decay can remove a third of compressive strength at 6 per cent mass loss,⁴ up to half of strength at 1 to 10 per cent mass loss,³ and does so before visible evidence.⁵

18.1 The comparison the extension literature makes

Fungal damage in the area of a persistent leak can be as threatening structurally as damage caused by the ants.¹¹

We would go further than that formulation on the evidence assembled here, and note it as our judgement rather than a sourced claim: in most structures where both are present, the fungus will have done the greater structural harm, and it will have done it first.

19. Control: the single variable

What the guidance says to do.

Finding the source of dampness and eliminating the ingress of moisture, whilst promoting drying, is always necessary.⁸

For the ants, since they favour moist wood as a habitat, any condition that promotes moisture should be eliminated to prevent infestation.¹³

19.1 The convergence

Two organisms from different kingdoms, with different biology and different damage mechanisms, have the same primary control measure. That is unusual and it is the most useful thing in this paper.

A moisture correction addresses the fungus, removes the habitat quality that attracts the ant, and prevents recurrence of both. No pesticide does any of the three.

20. What a pesticide cannot do here

Stating the limit plainly, because it runs against the commercial interest of this publisher.

An insecticide applied to a carpenter ant colony addresses the insect. It has no effect on the decay fungus, no effect on the moisture source, and no effect on the strength already lost from the timber.

20.1 What the client is left with

A successful ant treatment in a structure with a moisture problem produces a building with no visible ants, ongoing decay, and a repeat infestation when the next colony finds the same favourable conditions.

The visible problem resolves and the structural problem continues, which is the outcome most likely to be recorded as a success by everyone involved.

20.2 What we think the correct service looks like

Treat the colony, because the client asked and the ants are real. Then measure moisture at the timber, report what was found, and say plainly that the ants are a symptom and that the decay is the matter requiring a builder rather than an exterminator. This is our position rather than a sourced recommendation.

21. The Manitoba position

What applies locally and what we cannot establish.

Canadian light-frame construction is softwood, which is the substrate S. lacrymans attacks.⁷ Basements with timber bearing on or against masonry provide the timber-and-mineral interface the organism exploits.⁶

21.1 The climate argument runs both ways

A long cold winter with low absolute humidity favours dry interior conditions. Deep frost, spring melt, ground water against foundation walls and heavy seasonal loading of basements with moisture work the other way.

We have not found a Manitoba or prairie survey of decay incidence in housing stock, and we are not able to say which effect dominates here. We flag this as a gap rather than resolving it.

21.2 The one confident statement

Carpenter ants are a routine service item in this province, and every one of those calls is an opportunity to take a moisture reading that nobody else is going to take.

22. Limitations and open questions

Two sources are encyclopedia entries. The initiation and maintenance thresholds, the humidity and equilibrium moisture figures, the mineral scavenging and the fruiting moisture range are cited from general reference works rather than primary literature.²⁶ They are consistent with the primary sources used elsewhere here, but they are weaker citations and we flag them as such.

Several sources are trade or industry association material. The guidance note and the dry rot article come from a property care industry body with a commercial interest in remediation work.⁷⁸

Two carpenter ant citations are patent background text. The colony size figures and the statement that nesting is not restricted to moist or decaying wood appear in patent documents citing Ebeling and Hansen and Akre.¹⁵ We have used them for the underlying attributed findings and note the unusual provenance.

The strength loss figures come from different fungi and timbers. The comparisons in §8 are across species and cannot be combined into a single ratio,⁴ and the study reporting them found no linear relationship across periods.

The satellite nest finding weakens the central argument. Set out in §17. If most structural infestations are in drier sound wood, the ant is a less direct indicator of local decay than §16 suggests.¹⁰

Sections 11.2, 16.2, 18.1 and 20.2 are our reasoning. The meter placement recommendation, the claim that the moisture finding is the more valuable deliverable, the judgement that the fungus usually does the greater harm, and the description of correct service are ours rather than sourced findings.

No Manitoba data. Stated in §21.1. We have no local incidence survey and no local moisture data for housing stock.

This is not a structural engineering assessment. Whether a decayed member requires replacement is a question for a qualified professional, and nothing here substitutes for one.

Our commercial position. This company sells carpenter ant treatments. This paper argues that the insect is frequently a symptom, that the fungus does more damage, and that the necessary remedy is building work we do not sell. We publish it because we think it is true.

23. Conclusion

Fungal decay arises because wood has become wet in excess of 20 per cent moisture content,⁸ with dry rot needing roughly 28 to 30 per cent to initiate but remaining active above 20 per cent once established,² and laboratory work putting colonisation at 21 per cent and degradation at 26.2 per cent.¹ Because brown rot takes the cellulose and leaves the lignin frame,⁵⁷ the wood holds its shape while losing its strength: 33 per cent of compressive strength at 6 per cent mass loss,⁴ and reported losses of 6 to 50 per cent at mass depletion of 1 to 10 per cent, before decay is visually evident.³⁵

The carpenter ant enters this as a consequence. It prefers moist wood affected by fungal decay,¹⁰ feeds on the fungal growth, finds the softened fibres easier to cut,¹¹ and needs the humidity because its brood desiccates.¹² Its presence indoors is most important as a sign that there is or has been a water problem.¹¹

Which produces a conclusion this trade is poorly arranged to act on. The organism that does the structural damage is not an insect, cannot be treated with a pesticide, and is diagnosed with a moisture meter that costs less than a single service call. The insect everyone pays to have removed is, much of the time, the only visible evidence that the real problem exists. A carpenter ant job where the technician finds the leak is worth more to the building than the treatment, and it is the part nobody is invoiced for.

References

1. Influence of initial wood moisture on the decay process by two brown-rot fungi. Maderas: Ciencia y Tecnología. Source for the reported minimum moisture contents in the decay literature, including Huckfeldt and colleagues (2005) reporting for Serpula lacrymans a 21 per cent minimum moisture content for sample colonisation and 26.2 per cent for wood degradation using the flask technique introduced by Schmidt and colleagues (1996); Ammer (1963) reporting a minimum moisture content of 30 per cent for Coniophora puteana on Norway spruce; Walchli (1980) giving a range between 40 and 70 per cent moisture content for optimal action of the basidiomycetes; and reports of degradation below the fibre saturation range at relative humidity above 96 per cent, and by Meyer and Brischke (2015) on wood with an initial moisture content above 19 per cent. https://www.redalyc.org/journal/485/48565417034/html/
2. Dry rot. Encyclopedia entry. Cited as a general reference rather than primary literature. Used for the statements that Serpula lacrymans and Meruliporia incrassata require an elevated moisture content of 28 to 30 per cent to initiate an attack on timber; that once established the fungi can remain active in timber with a moisture content of more than 20 per cent; and that at relative humidities below 86 per cent growth of S. lacrymans is inhibited although it can stay dormant down to 76 per cent, these corresponding to equilibrium moisture contents of wood of 19 and 15 per cent respectively. https://en.wikipedia.org/wiki/Dry_rot
3. Dirty Rotten Fungi. CLM Magazine. Trade and claims industry source. Used for the account that researchers with the United States Department of Agriculture Forest Products Laboratory describe three to five progressive stages of wood decay under varied and localised conditions; for the description of early or incipient decay as characterised by slight to moderate discoloration such as bleaching or darkening of the grain, sometimes imparting a blotched or mottled appearance, with the surface exhibiting a sheen and appearing persistently wet as the mycelium advances and with dimensional changes minimal; and for the statement that strength loss varies widely by fungal species and wood type with reductions of 6 per cent to 50 per cent when mass is depleted by 1 per cent to 10 per cent. https://www.theclm.org/Magazine/articles/Dirty-Rotten-Fungi/928
4. Characterization of the Biodeterioration Caused by the Fungus Serpula lacrymans in Lignocellulosic Materials of Building Envelopes. Buildings, 15(24), 4513. Source for the description of S. lacrymans as considered the most aggressive and harmful brown-rot fungus for wooden buildings worldwide with substantial associated economic losses; for the study design inoculating radiata pine, CCA-impregnated radiata pine, raulí, oriented strand board and plywood and evaluating compressive strength at 0, 30, 60 and 90 days; for the reported mass loss of 6 per cent at 12 weeks with a decrease in parallel compression strength of 33 per cent; for the reported compression strength loss of 50 per cent at 20 per cent mass loss for wild pine attacked by Coniophora puteana; for the strength loss to mass loss relationship of four to one established for southern yellow pine exposed to Gloeophyllum trabeum for 72 days; and for the authors' observation that no linear relationship was observed across the various periods evaluated, with the most significant relationship obtained with incipient attack at 30 days. https://www.mdpi.com/2075-5309/15/24/4513
5. Brown Rot Fungus: an overview. ScienceDirect Topics. Reference compilation. Used for the statements that brown-rot fungi depolymerise cellulose rapidly during incipient stages of wood colonisation; that considerable losses in wood strength occur very early in the decay process, often before decay characteristics are visually evident, attributed to Wilcox (1968); that cell wall carbohydrates are degraded extensively during decay leaving a modified lignin-rich substrate with residual wood brown and often cracking into cubical pieces when dry; and that brown-rot fungi commonly cause decay of timber in buildings with serious impact on ancient and historic buildings. https://www.sciencedirect.com/topics/immunology-and-microbiology/brown-rot-fungus
6. Serpula lacrymans. Encyclopedia entry. Cited as a general reference rather than primary literature. Used for the statements that a moisture content of 30 to 40 per cent is the ideal level in wood to promote fruit body formation; that the fungus appears to require an environment where both inorganic and organic materials are present; that it uses calcium and iron ions extracted from plaster, brick and stone to aid the breakdown of wood; and that although a common indoor biodeterioration agent it has been found in only a few natural environments. https://en.wikipedia.org/wiki/Serpula_lacrymans
7. Dry Rot Insights: Fungal Growth in Buildings. Property Care Association research article. Industry association source with a commercial interest in remediation. Used for the description of S. lacrymans as well known for destroying timbers in buildings and spreading from floor to floor through hidden spaces, with its appearances leading to an almost mystical fear of its destructive abilities; for the corrective that it is only a woodland fungus that happens to have developed a capacity to grow in buildings, with an ancestral habitat of cool pine forests feeding on fallen dead wood on the moist forest floor, and that a building containing softwood embedded in damp masonry provides damp softwood to feed on, a moist surface from which to scavenge mineral nutrients and damp enclosed spaces to grow in; for the statement that it affects softwood and can be identified by visual inspection and if necessary analysis of decayed wood when sporophores are absent; for the account that early tensile strength loss occurs in wood that may still appear intact because the enzymes extract sugars from cellulose without at first disturbing the lignin framework, with genomic analysis showing scores of cellulose-digesting enzymes synthesised when hyphae meet wood; for the progression by which wood becomes brown, breaks into cubes by transverse and horizontal cracks and collapses into a dry brown powdery lignin residue; and for the observation that painted timber surfaces such as skirting boards are usually colonised by mycelium growing through damp underlying masonry. https://www.property-care.org/articles/dry-rot-insights-fungal-growth-in-buildings-pca-research
8. Guidance Note: Fungal Decay in Buildings. Property Care Association. Industry association guidance with a commercial interest in remediation. Used for the statement that fungal decay always arises because the wood has become wet in excess of 20 per cent moisture content and that finding the source of dampness and eliminating the ingress of moisture whilst promoting drying is always necessary; for the identification of true dry rot Serpula lacrymans, cellar fungus Coniophora puteana and pore or mine fungus Fibroporia vaillantii as the best known wood-destroying fungi with many other species affecting exposed or internal timbers and some particularly linked with decay in joinery, door and window frames; for the statement that dry rot is the most serious form of fungal decay and can spread into and destroy much of the timber while wet rot occurs more frequently but is less serious with decay typically confined to the area where the timber has become wet; and for the description of the mycelium as a mass of cotton wool-like growth with bright lemon-yellow patches in still humid conditions, water droplets on its surface giving the species its name, lilac tinges more common in less humid situations where surface mycelium is reduced to a thin silken grey skin, and thicker strands developing within the mycelium that supply water and nutrients to the growing front. https://www.property-care.org/media/ytedyezl/fungal-decay-in-buildings.pdf
9. Serpula lacrymans, Wood and Buildings. Research review. Used for the statement that a problem in controlling building dry rot is that the determinants of its destructiveness are not known, meaning what particular characteristics make it more damaging to buildings than its close relatives and other wood decay fungi which inhabit forests; and that its ability to infect and colonise timber in buildings has long been linked to a capacity to survive and flourish in a spatially discontinuous moisture and nutrient supply, an adaptation probably honed during its evolution from ancestors that grew in temperate and boreal regions. https://www.researchgate.net/publication/221805705_Serpula_lacrymans_Wood_and_Buildings
10. Ant Control: New Research Busts Old Myths. Pest Control Technology. Trade publication. Used for the statements that carpenter ants nest in wood structures and prefer moist wood affected by fungal decay but will also nest in sound wood and non-wood construction materials including foam and fibreglass insulation, drywall and particleboard; that the queen, eggs, early-instar larvae and workers are located in the parent nest, usually in a standing live or dead tree, rotting wood or a wooden structure, while workers, mature larvae, pupae and winged reproductives are found in satellite nests often excavated in drier solid wood; that satellite nests can be numerous, are often difficult to locate by visual observation alone and may account for as much as 75 per cent of structural infestations; that the most common route of invasion is a mature colony nesting outside setting up a satellite nest inside; that promoting conditions include proximity to forest, wood in contact with soil, vegetation in contact with the structure, roof or gutter leaks and infested trees on the property; and that the great majority of carpenter ant species are not pests and are highly beneficial, helping to recycle decaying wood and preying on forest pests. https://www.pctonline.com/article/-ant-control--new-research-busts-old-myths/
11. Carpenter Ants. University of Maryland Extension. Extension source. Used for the statement that the existence of a carpenter ant colony inside a structure is usually most important as a sign that there is or has been a water problem; that the damage of wood-rotting fungi in the area of a persistent water leak or seepage can be as threatening structurally as damage caused by the ants; that unlike termites they do not feed on wood but cause damage by creating nests in damp or moisture-compromised wood, with galleries extended into sound dry wood once a nest is established; that tunnelling may cause serious structural damage in key timbers but nest sites rarely exceed a few square feet; that damp or rotting wood is especially attractive because the ants feed on fungal growth and the softer fibres make tunnelling easier; and that excavations look sandpaper smooth and are kept very clean, unlike termite galleries which are packed with mud and excrement. https://extension.umd.edu/resource/carpenter-ants
12. Carpenter Ants: an overview. ScienceDirect Topics. Reference compilation. Used for the statements that carpenter ants prefer higher moisture content and softer wood that has begun to decay but will invade sound wood; that unlike termites they do not digest wood but use it as a nesting site providing a habitat that can be kept moist since the immature stages are subject to desiccation; that moisture is essential for their activity in wood and that they supply moisture as needed by transporting it from the soil through tunnels; that mature colonies may contain as many as 3,000 members; and that wood particles are expelled from holes or slits made in the surface with sawdust piles constituting evidence of infestation. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/carpenter-ants
13. Black carpenter ant. Encyclopedia entry. Cited as a general reference. Used for the statements that in their natural environment carpenter ants nest in dead trees and other dead wood which enhances decay and has ecological benefits; that since they favour moist wood as a habitat any condition that promotes moisture should be eliminated to prevent infestation, the easiest being keeping gutters clear so that water does not run down the side of the structure; and that moist wood is much easier to chew, with the ants removing rather than eating it and galleries running parallel to the grain in the softer, non-aligning portions of the timber. https://en.wikipedia.org/wiki/Black_carpenter_ant
14. King, J.R. and colleagues. Ants: Ecology and Impacts in Dead Wood, chapter 8. Used for the statement that most ant species lack the ability to excavate sound wood, with the exception of carpenter ants in the genus Camponotus, and more commonly occupy preformed cavities excavated by wood-boring beetles or termites; that channelization typically occurs after trees are mechanically damaged, followed by the initial stages of wood decay when fungi attack the pith, bark and wood surface; and that as wood becomes more decayed and soft, species other than Camponotus may then be able to excavate it to create nests. https://sciences.ucf.edu/biology/king/wp-content/uploads/sites/14/2018/05/King-et-al-2018-ants-in-dead-wood.pdf
15. Background material on Camponotus biology appearing in United States patent specifications, citing Ebeling (1978) Urban Entomology and Hansen and Akre (1985), Biology of carpenter ants in Washington state, Melanderia 43. Unusual provenance, cited for the underlying attributed findings only. Used for the statements that preference for moist or decaying wood has been reported but that nesting sites are not restricted to such areas; that more significant damage occurs when carpenter ants extend their nests into sound wood; that carpenter ant populations develop relatively slowly with colonies of 300 to 2,000 workers produced over a two year or longer period; and that worker movement occurs between the main colony and satellites which serve as areas for further brood development and colony expansion. https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/6403085