How To Treat Woodworm (and prevent it coming back)

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You approach your roof timber, floor board or beautiful piece of solid wood furniture. You look closely, and there it is. Tiny little holes bored into the surface. You brace yourself, and turn to the internet. ‘How to treat woodworm’.

Thankfully then this guide pops up and you relax, because I’m here to tell you exactly what to do to get woodworm-free.




Tools and Materials Required


  • Bucket (if mixing insecticide powder with water)
  • Drill (if dealing with Deathwatch beetle)
  • Gloves
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    Sprayer (for liquid solution)


  • Brush (for gel solution)


  • Applicator gun (for paste solution)
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    A second brush for paint or varnish


  • Insecticide; either boron (in powder, gel or paste form) or permethrin
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Follow steps 1 and 2, then move to Step 3 of the set of instructions for the type of woodworm you have.

Check for woodworm


First of all, woodworm isn’t a worm, it’s a beetle. Small holes in the wood made by larvae actually mean the woodworm is advanced, as the larvae has already turned into a grown beetle.

The beetle flies out of the hole, but returns to lay more eggs, that turn into larvae. Keep watch for frass, which looks like sawdust, as this is evidence the larvae are active.


Pro Tip: Peter Cox suggests hanging fly strips in roof rafters to catch adult beetles and kill them

Identify woodworm

Now you know you have woodworm, check which type it is, as the treatment methods are different.

The common furniture beetle is, unsurprisingly, the most common type, the death watch beetle sounds scary but is reasonably easy to treat, while the longhorn beetle requires a professional bug killer.

Holes 1-2mm across surrounded by fine sawdust (actually a waste product called ‘frass;) indicate the common furniture beetle, while larger holes and large pellets mean you’ve got the deathwatch beetle (not as scary as it sounds). Tiny holes and sticky frass suggest the longhorn beetle.

for Common Furniture Beetle

Indicated by holes 1-2mm across. Frass will be very fine.

Choose your insecticide spray

furniture beetle

I recommend Boron instead of Permethrin, as the latter is a man-made chemical that is harmful to the environment and can kill animals as well as insects. Do not use Permethrin in a house with pets.

Protect yourself

Insecticides are dangerous, so put on a mask and goggles to prevent irritation.

Dilute powder

If using a boron based solution, dilute according to manufacturer’s instructions. This is likely to be 1 kg of boron powder to 25 litres of water. You can buy ready made solution.

Apply first coat

​Spray solution onto wood, giving a thorough coating. Pre-made solutions often come with a sprayer attachment. Leave to dry.

Apply second coat

Spray a second coating when first is dry, usually after a couple of hours, but check the manufacturer’s instructions to be sure.

Apply gel

For heavy patches of infestation, apply the boron solution in a pre-mixed gel. 1 litre of gel provides coverage for 4 square metres.

For Deathwatch Beetle

Indicated by holes 3mm across or larger and pellets of frass.

Locate the infestation

​Tap the infected wood to see which areas sound hollow, this is where the infestation is.

Drill test holes

drill test holes

Drill holes around the edge of the infested areas to accurately work out how big a patch you are dealing with.

Drill more holes

​Drill holes in a diagonal polka dot pattern across the area that are 10mm wide. Drill down until 15mm from the other side of wood.

Fill holes

Fill holes to the top with boron paste using an applicator gun. 


Pro Tip: The DIY Doctor recommends attaching a small length of plastic tubing over the nozzle of the paste container for greater accuracy.

Insert dowels

Push dowel inserts into filled holes to trap boron paste. Use a cloth to wipe away excess.

Apply gel

Coat the outside of the wood with boron gel, allow to dry and apply a second coat.

For Longhorn Beetle

Indicated by very small holes and frass that appears sticky (as though it has been mixed with wood sap).

Check hole size

Commonly found in roof timbers, longhorn beetle holes are larger than the 1-2mm made by the common furniture beetle.

Do your research

Check the Building Research Establishment (BRE) to see if longhorn activity has been reported in your area.

Contact a professional

If you think you have longhorn infestation, then you need to contact a professional for removal. The chemicals involved are not safe for a DIY job.

Prevent Woodworm From Returning

Having gotten rid of woodworm, you don’t want it coming back, so here’s a couple of tips to help you stay woodworm free:

  • Keep your house well-ventilated. Woodworm love the damp, so keep a close eye on any timber that is in a damp environment.
  • It is easier for beetles to bore into wood that doesn’t have paint or varnish on it, so maintain these items regularly.

Hopefully you are now on your way to being woodworm free. Regular woodworm isn’t difficult to tackle, and it doesn’t need to be the end of your home or furniture. Being infested once doesn’t mean you will have a second infestation if you take the proper precautions.

About the Author Vicky

Blogger who spent childhood suffering through many house renovations, but at least now is old enough to design rooms to her taste