The deathwatch beetles started knocking and emerging late this year. It was around the middle of April rather than late March.
I've been collecting the beetles and counting them. I think they are in decline. I would estimate on average I've collected 100 per week. They are still emerging now at the end of May but the knocking has pretty much stopped.
I've been studying where they are emerging from and have measured the moisture content of the wood.
When I bought the property it had a bit of a problem with damp on the dwarf wall which the sole plate rests upon. The company doing the damp treatment and woodworm treatment recommended tanking (covering in plastic) the interior wall. This has stopped the damp but I think has increased the deathwatch beetle problem. Rather than the water evapourating in the air, the water is now trapped in the brickwork and rising to the sole plate via capillary action.
The sole plate now has a nice supply of water to feed the deathwatch beetles.
Deathwatch beetles need a wood moisture content of at least 14% to survive. The moisture content of the wood at the boundary with the brickwork is 22%.
The exit holes are more dense near the boundary hence I think with hindsight that tanking was the wrong solution and would have also saved me a reasonable cost!
Some articles on the web suggest that the survival of deathwatch beetles is usually down to some building defect such as cracks, leaks or down-pipes. I've measured the water content of internal beams where it would be impossible for a building defect to allow water to ingress and the beams measure about 18%. So at a level where deathwatch beetles can survive.
The wood was treated when I bought the house and the majority of exiting beetles are being killed by the poison. I am straying into the exit holes with a long straw like sprayer, crawling insect killer which contains permethrin. This seems to be working too.
Why am I spraying when it's been treated? Well I've discovered that traditional wood worm treatment is a surface spray and penetrates the wood only a few millemetre. Occassionally I find very deep deathwatch beetle exit holes which are 2-3cm deep.
Not all beetles exit to reproduce. It's been recently discovered that mating can occur in the holes and therefore the lavae continue munching on untreated wood.
By spraying into the holes, the poison is delivered deep in the wood and onto any beetles or lavae in there. I don't know if this strategy is working but it intuitively seems a better approach than relying on them exiting.
Square wood has four faces. When the building was treated only the exposed faces were sprayed so in some cases only one face (25%) of the wood has been treated.
I don't know whether all the beetle tapping allows these pests to emerge on the face - if not then I only have 25% protection!
I've got the dehumidifier running when my wife is not around to complain about it. That should help in drying out the wood and removing that all important water for the death watch beetle survival.
Beams by radiators have a moisture content of 0% ! And no sign of deathwatch beetle either. Removing moisture is clearly a good strategy.
So in summary I think they are declining compared to previous years but the emerging season hasnt finished yet. We are now 6 complete years after they have been sprayed which is cited as the breeding cycle so next year hopefully will see a significant decline in beetles.
