Woodworm Larvae: What They Look Like, Size & How to Find Them

Woodworm larvae are the grubs that do the damage. They live inside the wood, so you almost never see them. This guide explains what they look like, how big they grow and how to tell whether they are still active.

What do woodworm larvae look like?

Most larvae are creamy white, soft and curved like the letter C. They have a small brown head and tiny legs. When fully grown, a furniture beetle larva is about the size of a grain of rice.

Other species look similar, though bigger grubs belong to bigger beetles. The house longhorn larva can grow much longer. The species guide compares them.

Where do the larvae live?

They live inside timber, in tunnels they dig as they feed. They prefer softwood sapwood, and they like wood that is cool and slightly damp. Some species, such as the death watch beetle, prefer old oak.

You usually find them in:

• Floor joists and floorboards
• Rafters and roof timbers
• Stair strings and skirting boards
• Old furniture and reclaimed wood

How do you find them?

You rarely see a live larva, because the wood hides it. You may find one where timber has split or been cut. In that case, the tunnels will be packed with fine dust.

You can usually tell they are present by indirect signs. Fresh dust under holes means larvae are working or adults have just left. Tapping the wood may sound hollow. A surveyor can also probe the wood or cut a small sample.

How long do they feed?

For the common furniture beetle, larvae feed for several years. The time depends on the temperature, the moisture and the quality of the wood. Cool, damp, low-nutrient timber slows growth. Our guide to the woodworm life cycle shows the stages in order.

How much harm do they do?

One larva eats little. A colony can riddle sapwood with tunnels, however, and weaken it. The damage is hard to judge from the surface. For that reason, probe suspect timber and look at the edges for crumbling.

Read is woodworm dangerous? for how to judge the risk.

Are the larvae still alive?

Dead larvae do no more harm. Check three things:

• Is fresh dust appearing?
• Are new holes forming in summer?
• Is the wood damp?

If the answer is yes, the larvae may be alive. If all three are no, the infestation has probably ended. The guide to active versus historic woodworm explains the dust test.

What to do about larvae

Treatment aims to kill larvae and protect the wood from egg laying. A spray reaches the surface layers, while paste reaches deeper. Read how to treat woodworm for the options, or request a survey for a firm answer.

Local housing changes the risk. Read about woodworm treatment in Edinburgh and woodworm treatment in Cardiff to see what affects homes in each area.

To go deeper, read about the common furniture beetle and the boron paste treatment, because the right method depends on the beetle.