Woodworm - Facts, Misconceptions, Myths and Old Wives Tales

[Cubist]

Finding myself at a bit of a loose end, and given the recent up-tick in discussions concerning Woodworm problems, now may be an opportune moment to open a discussion concerning these beasties. I, like many others I suspect, have never made a particular study of these pests and have therefore relied on the opinions of others - and what I've found on the backs of the relevant tins - to inform my efforts to eradicate them when discovered. However, I have often found myself shaking my head and thinking - "That just does not make logical sense! or "What's this guy been smoking?" and on notable occasions finding myself chuckling over an image that popped into my head; the most recent of which was of a beetle wandering through a forest of chair legs tapping on each one until it finds one made of its preferred elm. They can't possibly be that discerning, can they?

But then, I can be a trifle cynical and all too willing to challenge conventional wisdoms - as implied by the handle I use for this website - and I may therefore simply be over-thinking it. So, in the hope of getting to some truths I and others can keep in mind for the future, my question to the members is; 'What are the facts and Which are the Myths? - Discuss please.

Starter for 10 - When you see the exit holes they're gone and will not come back.

 

[Toby Newell]

Wrong. Or moot. As even if genetically they are programmed to fly to new pastures, others will do the same and arrive where others have left. If it were not so you would only see low damage, often you see massive damage, I have seen joist eaten out to thin air. From my survey of several hundred (possibly a thousand?) properties I can say you get worm in most woods, pine oak and elm. In boards you can get them anywhere (starting at the sapwood) but in joist and beam mostly in the sapwood. This can make it look worse than it really is as many very old rural timber framed houses were made with waney edge green oak / elm hence a lot of sapwood.

Common Furniture Beetle seems the most common, they seem to like floor boards and floor joists, Post Beetle and Death Watch Beetle seem to like beams, I have occasionally seen post beetle galleries in floors but not death watch.

It would appear CFB prefer pine unless the hardwood is very damp or partially rotted, DWB prefer hardwoods, it seems.

I have not noticed a preference of PB and DWB between the hardwoods.

As someone else noted, I cannot recall seeing worm damage in pitch pine. I guess some of the terpenes in the resin have similar anti pest properties to cedar oil.

Having completed many, many hundreds of jobs where I have encountered worm I cannot recall using a treatment more than a dozen times, probably less, there is simply no need.

Reducing damp kills worm and keep it at bay far more effictively than applying poison.

As long as the timber isn't weakened by them I like flight holes and the meandering galleries, it's a virtually unfakeable (they do try with dentists drills) mark of age and adds greatly to the patination.

 

[Toby Newell]

There is no edit feature anymore, so,

Edit: Worm start off in sapwood and if damp enough move to the heartwood, it is common to get galleries all throughout boards and small dimension joist (up to 4in wide) especially pine. For larger joist and beam the CFB and PB worm mostly stay in the sapwood. DWB seem happier to munch right through the (oak and elm) members, hence their reputation.

 

[Zebra]

Well, I will get shot down for this, and I'm not meaning to argue with anyone specifically, but I wish to question the idea that they will not appear in dry wood. This post is right in front of the fire, and it is stood on concrete with a DPM. Those holes were not there two years ago. They have mostly appeared this year.
It is reclaimed timber and was in a dry shed for several decades before I put it in its current location around 8 years ago.

 

[Matt Green]

Well, I will get shot down for this, and I'm not meaning to argue with anyone specifically, but I wish to question the idea that they will not appear in dry wood. This post is right in front of the fire, and it is stood on concrete with a DPM. Those holes were not there two years ago. They have mostly appeared this year.
It is reclaimed timber and was in a dry shed for several decades before I put it in its current location around 8 years ago.

I'll reply more Cubist, I promise, but this is great.

Okay, so let's work this back: No hole two years ago, and all the beetles have just flown out of a clearly demarked piece of sapwood/heartwood differentiated timber. The larvae have excised to adults, boring their way out and flying off. 2-5 years ago that sapwood surface was wet enough for female furniture beetle to lay eggs in. It's been in it's location for 8 years and furniture beetles go through their lifecycle in 2-5 years. Probably closer to 5 in this case- it must be pretty dry.

That's fascinating. I would certainly have bet against it. Do you have a resistance (%m/c) reading for the sapwood and heartwood sides Zebra?

 

[Toby Newell]

^^^ that, beetle are very, very moisture dependent most probably the area it was kept in was not quite as dry as you thought. Remember dry as in not leaky is not necessarily dry and in not slighter more humid than a heated house.

You say dry shed, I say "dry" shed, sheds are rarely as low humidity as heated homes. Post not that old, has modern machine saw marks.

More importantly though, your floor (and post) what is with all the white pastiness? Have you been possibly overdoing the wax a tad? The white in the flight holes would suggest so.

 

[Zebra]

I don't have those readings I'm afraid Matt, but I appreciate your interest in the question. Like many of us I don't overheat my home, especially when I'm not in it, so the temperature can drop to 15 degrees indoors in the winter, perhaps affecting the RH and feeding into your point, Toby, that "dry" and "damp" are not quite absolute terms. But the fire is lit every evening in the winter, bringing the ambient temperature at the post location up to, well, I don't know, you can imagine, warm....
The white in the holes, no that's not wax, that's just the flash on the camera lighting up the sides of the holes. I did fill the first few holes that appeared two years ago with beeswax just so I would know for sure if new ones appeared. But most are empty holes.

Amendment: post went in in 2013, ten years ago.

 

[Toby Newell]

Yes. Less dry. More damper (sic). Sheds are inherently more damper. Unless of course they are not really sheds, but posh log cabin style shed with heating. Yes, almost certainly your rh is higher than you think.

 

[Cubist]

Well that figures, harumph, I report that I'm at a loose end and suddenly... I'm reeled in and have a new list of ToDos!

That aside, my Starter for 10 question was always on my 'Myth' list but I have to admit there was a poorly hidden subtlety to it as I believe the answer can be both Yes and No. Yes, because a generation of adult beetles have fled the scene and will not return because they died within a couple of weeks and No, because there may be other, younger, generations of larvae still in residence in the timber or a new generation may have been implanted by impreganted females from the generation that only recently surfaced. Ergo, the only thing we can perhaps say for sure is that that one generation of woodworm is probably dead and gone but theres no guarantee that another won't surface from the same timber. One of my other reasons for pushing back on this maxim is consideration of the network of tunnels and chambers excavated by the old generation as, to my mind, these must fill with air which in turn carries moisture that is then absorbed through the vastly increased available internal surface area of the wood and therefore perhaps making it even more attractive to later generations. Ok, convoluted I know but does that not make sense?

So... can we put that one in the 'old chestnut' box?

Zebras post, the oak one not the reply, is very curious indeed, particularly if one accepts the five year upper limit on the larval stage of woodworm. I think there are a couple of possibilities concerning where, when and how this latest infestation arose but Zebras reply also points to one of the other claims I regard with some suspicion. That being; woodworm will not infest 'dry' timber and Zebras post (the oak one) seems to provide conclusive proof that that claim too is false. Can anyone refute that evidence? Alternatively is there some specific threshold of dryness that needs to be achieved and maintained to be confident that the beetle community will move on to greener pastures?

Got to go, ToDo list beckons.

 

[Matt Green]

"That just does not make logical sense! or "What's this guy been smoking?" and on notable occasions finding myself chuckling over an image that popped into my head; the most recent of which was of a beetle wandering through a forest of chair legs tapping on each one until it finds one made of its preferred elm. They can't possibly be that discerning, can they?

Sure they can. Scots Pine emits:

whereas oak smells of:



Some are the same, some are different and it's a cocktail.

Poleven et al 2019 Wood and Fibre Science:

https://zenodo.org/record/3357750/files/VOLATILE%20ORGANIC%20COMPOUNDS.pdf?download=1#:~:text=Wood%20VOC%20emissions%20are%20dominated,acid%2C%20hexanoic%20acid%2C%20and%20formic

Insects live in a different sensory world to us and different timbers smell different, particularly if they are damp/wet/decayed just as clothing does to us when it is in a similar state. You can test it pretty easily if you are so inclined:

and you run wood-boring weevils in that apparatus for several weeks and you get:

...and there is a statistically significant preference for alpha-pinine and ethanol for wood-boring weevils.

Me, 2004 PhD Thesis.

 

[Matt Green]

When you see the exit holes they're gone and will not come back

Myth or moot. If you are an adult beetle that has emerged from timber that was soft and full of nitrogen and you gained loads of energy and pupated quickly- and the timber is still in the same condition, then why not lay your eggs in it?

Yes, because a generation of adult beetles have fled the scene and will not return because they died within a couple of weeks and No, because there may be other, younger, generations of larvae still in residence in the timber or a new generation may have been implanted by impregnated females from the generation that only recently surfaced. Ergo, the only thing we can perhaps say for sure is that that one generation of woodworm is probably dead and gone but there's no guarantee that another won't surface from the same timber. One of my other reasons for pushing back on this maxim is consideration of the network of tunnels and chambers excavated by the old generation as, to my mind, these must fill with air which in turn carries moisture that is then absorbed through the vastly increased available internal surface area of the wood and therefore perhaps making it even more attractive to later generations. Ok, convoluted I know but does that not make sense?

Yes, that's entirely reasonable. Deathwatch beetle do it pretty regularly.

 

[Matt Green]

Common Furniture Beetle seems the most common, they seem to like floor boards and floor joists, Post Beetle and Death Watch Beetle seem to like beams, I have occasionally seen post beetle galleries in floors but not death watch.

It would appear CFB prefer pine unless the hardwood is very damp or partially rotted, DWB prefer hardwoods, it seems.

I have not noticed a preference of PB and DWB between the hardwoods.

As someone else noted, I cannot recall seeing worm damage in pitch pine.

Seems totally reasonable. More beams that are preserved in period buildings and exposed are oak than softwood and there are many more meters of softwood board out there than oak.

Do you ever see Pitch Pine though, as in: Pinus rigida? I ask because outside of marine use, its hen's teeth rare over here due to the size of the trees and the cost to import.

Edit: Worm start off in sapwood and if damp enough move to the heartwood

They have to wait until all the cold water extractives, tannins and polyphenols have leached out, but yes- once that happens and the physical structure gets softer and more chewy they can move in.

<- the sapwood is gone. This is as far up the beetles got in the heartwood->

Spent an afternoon sawing at 5mm intervals to get that.

 

[Matt Green]

I don't have those readings I'm afraid Matt, but I appreciate your interest in the question. Like many of us I don't overheat my home, especially when I'm not in it, so the temperature can drop to 15 degrees indoors in the winter, perhaps affecting the RH

Oh, no worries. I don't have all the answers, I just find it fascinating to try and work it all out. There are so many different variables that there will always be a gotcha out there but there is always a reason for it. As long as we agree that: it's not random- the beetles know something we don't then we can start asking interesting questions and keep learning.

For Scots Pine as a starting point:

Air temperature at 15C or lower could see 70%-80% rh at night, depending where you are and how much rainfall you get. Maybe it was one bad year that tipped it over the edge? Strange that it's suddenly happened after 10 years. Could be a chemical change in the timber- after a while, the volatiles will change and it will smell slightly different- I'd need aa headspace GC to find that out though. The air next to the heartwood surface should smell different to the sapwood surface unless the eggs were laid randomly and just didn't develop on the heartwood. Seems unlikely but I'm not sure.

Furniture beetles lay eggs in batches of about 30 so you have had a few different egg-laying instances in that post.

 

[Matt Green]

Zebras post, the oak one not the reply, is very curious indeed, particularly if one accepts the five year upper limit on the larval stage of woodworm.

And maybe we shouldn't. That's an average

This is interesting:
https://unsworks.unsw.edu.au/bitstreams/157360e5-e601-4e5f-adc4-15b81b778315/download

It's a masters thesis about factors influencing furniture beetle life cycle and there are several references in there for larvae being found alive after 5 years so it shouldn't be an absolute, and Zebra's post has been in situ for 10 years. 2-3yrs in a lab under controlled conditions has been achieved as a lower limit but no one has tested the upper limit, so there is likely to be a lot of grey and the top end. Fair point.

IZebras post (the oak one) seems to provide conclusive proof that that claim too is false. Can anyone refute that evidence? Alternatively is there some specific threshold of dryness that needs to be achieved and maintained to be confident that the beetle community will move on to greener pastures?

Don't be ridiculous, it's one instance, that's not conclusive in any fashion and nobody is dealing in absolutes on a forum designed to stop people making bad decisions about period property repair. If you take it to an absurd end point you would spray all timbers every year.

Brian Ridout does a pretty good job of collecting up the academic literature in Timber Decay in Buildings (2000):





but again, we are dealing with averages, not absolutes, which is what makes Zebra's post interesting- what is going on? As I said above, as long as we agree that site selection and egg laying by a female beetle is a non-random event there must be or have been something in the physical/chemical make up of that one side of the post that resulted in female beetles finding it and successfully laying eggs in it. It's madness- how did they find it? Which VOCs were they responding to and in what concentrations? I don't know- but I would love to find out.

 

[Zebra]

Well I've treated it now with pemethrin stuff, used a syringe to squirt it in all the little holes to try to penetrate past the surface.
Perhaps I have high RH. According to my little thermometer/ RH meter, right now in that room it is 20 degrees C, 73% RH. It would seem from googling that that is higher than average. In the winter the temperature averages less, but the RH tends to be similar. I always shut the bathroom door and open the window after creating steam in there, and don't boil pans on the stove for ages (kitchen and living room are open plan)...... Doors and windows are often open all day. So I don't know why it would be so high. I can get it down with a dehumidifier but it uses a lot of energy obviously to run it all the time, and seems pointless if the windows and doors are open.

 

[Toby Newell]

Matt makes some good points. Excellent work there. Quite possibly things are not exactly as Zebra recalls, memory does that, also there are always outliers, so even though the life cycle might be 2 to 3 years in good conditions and many have been found after 5 years it seems quite possible, than in extremely rare circumstances they could last for longer. Science only describes what is currently known, maybe the researchers should visit Zebra XD.

My additions to this topic are totally subjective, albeit informed by over three and a half decades working with wood, two and a half of them as a professional wood restorer, so my population size for my qualitative analysis is in the high hundreds or more.

I was not aware how low the moisture content has to be stop worm hatching, that is very interesting 10 to 12% would feel dry to most people, 10 to 12% is how normal yard stored timber or that stored in a shed comes, so very likely indicates the worm proliferated in Zebras' shed. The same chart says few / no eggs hatched at 8 to 10%, from that we can deduce that it is possible for eggs to hatch at at 8%, that is amazing, once you open the packet on kiln dried timber to let it breathe it is 8%, only in winter with central heating would it be lower. It would seem there must be other factors apart from moisture content

Do you ever see Pitch Pine though, as in: Pinus rigida? I ask because outside of marine use, its hen's teeth rare over here due to the size of the trees and the cost to import.

In beams? not very often, you do see them, in kitchen areas or in later additions, I have seen a few but not many, I would say in my experience around 90 to 95% are oak, 5 to 10% elm with a few pitch pine ones thrown in there. It is important to note that there is a difference between country and town dwellings, you are more likely to find oak and elm in the country where the timber used was presumably local, whereas in town more imported pine was used. Floors? relatively often (still rare compared to yellow pine or oak even) Churches are full of it! I regularly see pitch pine, I would say, in my experience (in the solid, discounting veneered items) I would say it goes yellow pine (spruce, larch etc) oak, pitch pine, various exotic hardwoods (iroko, teak, sapelle etc) then elm. Quite a lot of pitch pine about. It's also not hens teeth rare! And how does it cost more than African and Asian hardwoods to import? It comes from North America!

They have to wait until all the cold water extractives, tannins and polyphenols have leached out, but yes- once that happens and the physical structure gets softer and more chewy they can move in.

Ok, now this makes me scratch my head, do you have a reference for this? I totally do not understand how this would work! Please explain. What you are saying is you have water soluble compounds in sapwood, tannins and polyphenols which are relatively immobile and they have to be "leached out" that requires submersion in water! Otherwise the solutes would not be free to pass. I can tell you, I have sanded and washed centuries old oak, still plenty of tannins left. From my degree level understanding of chemistry and physics that seems impossible. Being damp doesn't remove tannins from the wood, it simply allows them to move through the wood. It is possible other polyphenols, being organic compounds, are more susceptible to breakdown and oxidation, but tannins? not so much in my experience. Btw, I never knew tannic acid was a polyphenol, so thanks for making me look it up.

So no, your term leaching is incorrect as most wood has not been submerged that has worm! It is quite possible that the polyphenol content (including tannins) is reduced under high moisture conditions as this might be favourable to their breakdown by other molecules found in the wood (or microbes) It is quite possible there is a threshold that needs to be reached for conditions to be favourable for worm, but that certainly is far above zero, as I say, I sand, strip and wash centuries old timber for a living and I can tell you 100% that several hundred year old oak can have plenty of tannins left, I can see them (tide marks, water goes grey beige if very clean or deep brown if dirty) taste them (yes, smell) and feel them (yes, astringent to the hands and make the skin tighten)

All great work.

I would like to add an intuition my work has given me. Microbes. I have found some wood looks perfectly normal but weighs much less (less dense) in fact I often lift boards to weigh them in my hand to see how viable they are. I can only assume microbes have eaten some parts of the wood, I am talking about fungi and bacteria. Not all wood "spalts" as in leaves traces, even wood that spalts is attacked long before the decomposition and metabolite lines and bleached patches appear. This must make it easier for worm to digest.

My totally subjective theory is that high moisture content favours microbial attack and it is this which consumes the polyphenols and provides food for the worm and reduces the density so it is easier for them to move. Worm cannot digest cellulose directly, they require gut microbiota to do that for them in vivo. I am suggesting the main mechanism promoting worm / beetle propagation is in fact moisture induced microbial proliferation that predigests cellulose in vitro for the pest. I have thought this for some time.

Thank you Matt for piquing my interest.

 

[Toby Newell]

Common Furniture Beetle seems the most common, they seem to like floor boards and floor joists, Post Beetle and Death Watch Beetle seem to like beams, I have occasionally seen post beetle galleries in floors but not death watch.

I would also like to clarify, I have seen DWB in boards, very rarely and in catastrophically damp, read wet, circumstances, it is not normal and they certainly don't really like pine and none of them don't seem to like pitch pine.

 

[Toby Newell]

Consider me Matt's on the spot reporter, whilst he is back at the studio at the controls doing all the technical stuff... I am on the road...

First and last photos are beam so bad I had to remove them all and fit new floor showing all three main beetle types.

Second, third and fourth photos are 500 yr + pine from Suffolk and yes, I saved every single board apart from a few sections that crumbled to dust.

I am trying to get my video of me scraping away the worm damaged sapwood from the solid heartwood on a 500yr + old oak bressumer uploaded but it seems I have to reduce the size further.

 

[Toby Newell]

For all those doubters, here is board number 6, ready for another half a millennia... 500 year old pine is incredibly rare for this reason, it gets eaten to death and everyone else throws it away. I know of no one else in the UK doing this sort of work and there are very few people willing to pay for it, but it's nice to occasionally do it. The client (Hi Aaron you lurker) is renting it out as as an air bnb bedroom (I can recommend, apparently he has fabulous wood in his c.15th house) I told him he should sell tickets as a sort of museum. It should be noted he spent months cleaning all the exposed beams and got all the walls totally replastered using wattle and daub and lime. Must be one of the best preserved c.15th rooms in the UK, incredibly hard work but uniquely rewarding. 300mm floor deflection, it's nearly as wonky as the wonky house in close by Lavenham.

 

[Toby Newell]

Whilst we are on the subject, despite a recent resurgence in interest, which might not make this totally accurate in a few years time, I find that Douglas Fir is rarer to find than pitch pine. Many church interiors were executed in pitch pine, parquet floors, pews etc, it's by far the most common wood to be found in old churches and rectories, possibly because the church always used to have money. Pitch pine was also used for domestic parquet floors and stairs. Douglas fir on the other hand was used for a few interior doors from the 1910's to 1930's.

I always call pitch pine an honorary hardwood, due to it's rarity and better qualities, I do like it, despite it being difficult to sand because of the pitch, with the exclusion of the very rare floor above and some very tight, fine grained old pine, I am not really a fan of pine, which is shame as I have restored so much of it. I guess that's why I like pitch pine so much. I do tell people as soon as I spot it that they are lucky as it is much rarer than oak for example.

I'm not sure you will get so excited over horrible, non worm eaten timber (has anyone told you you're weird?) but here is rather lovely pitch pine parquet in Wimbledon laid in wonderful bitumen, floor was damp at some point, hence many blocks had to be laboriously scraped, but the blocks didn't shrink that much and no worm damage.

I seem to recall slight pimples on the sealer, on close inspection once the top was sanded and the fresh resin was exposed it, er exuded, you must use shellac barrier seal, luckily I do, and seal it straight away, which I did, at night, the pitch was strong in this one. Does smell nice though.

I guess woodworm are quite fussy eaters, they love the smell of pine aromatics, but not too much!