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Mud tubes: what they are and why you must not break them

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A mud tube is the clearest evidence you will ever get that termites are working on your house. It is also the easiest thing in the world to destroy by accident.

Why a termite builds a road

Subterranean termites cannot survive in open air. Workers have thin, unpigmented cuticles and lose moisture fast, so they will not cross an exposed surface. When their food is on the other side of something they cannot eat through (a brick pier, a concrete stump, a steel post, a slab edge), they do not go around. They build a covered tunnel over it out of soil, saliva and faeces, and travel inside.

That tunnel is a mud tube (also called a shelter tube or a workings tube). And it is the single most useful sign in this whole subject, because it is unambiguous. Nothing else in an Australian house builds a pencil-width mud highway up a wall.

Where they actually appear

They appear wherever the termite has to cross something inedible, which in practice means a short list of places worth checking:

  • Subfloor piers and stumps: the classic location, running up brick or concrete to the bearer above.
  • The slab edge and the perimeter, especially where a path, a garden bed or a paved area is built up against the wall.
  • Weep holes in brickwork, which are an open, sheltered entry into the cavity.
  • Inside the cavity itself, where you will never see them: which is exactly why concealed entry is the thing barriers are designed to prevent.
  • Retaining walls, fence posts and stumps in the yard, running from the soil into the timber.
  • Down from the ceiling, occasionally, when a nest is above and workers are descending: an unnerving sight and not a rare one.

Active or abandoned?

This is the question everyone asks, and the honest answer is that it is harder than it looks from the outside. The rough guide is that an active tube tends to be damp, dark and intact, and an abandoned one is dry, pale, brittle and often already broken. Old tubes can sit on a pier for years after a colony has gone.

But that guide fails often enough to be dangerous. A colony can be active in the building and not using that particular tube. A tube can look dry on the surface and be in use behind. And the reverse mistake (deciding a dry tube means an old, resolved problem) is how people talk themselves out of an inspection.

What you must not do

The instinct on finding a mud tube is to break a piece off and see what is inside. Please do not.

Termites respond to a breach in their workings as a threat. The colony seals off the damaged section, abandons that route, and re-establishes access somewhere else in the building. Somewhere you are not looking, and quite possibly inside a wall cavity where nothing will be visible until the damage is severe. You will have converted a problem that announced itself into a problem that hides.

Spraying the tube with a supermarket insecticide is the same mistake with an extra cost: it kills the workers in that runway, produces exactly the same abandonment response. And removes the foraging population that a professional treatment would have relied on to carry a product back to the nest. See why spraying termites yourself makes it worse for what that does to the treatment options.

What to do instead

Leave it exactly as it is. Photograph it, note where it is, and get a timber pest inspection. If the tube is somewhere it could be knocked accidentally (a doorway, a path, a spot the dog goes past) put something in front of it rather than moving it.

Then look at the rest of the property, because a tube tells you there is a colony nearby with a reason to come here. And the reason is usually moisture or timber in ground contact. Risk factors covers what to look for.

Frequently asked questions

Does a mud tube always mean termites are in my house?

It means termites are travelling over that surface to reach timber. Whether they have reached structural timber, and how far they have got, is what an inspection determines. A tube on a fence post is a different situation to a tube on a subfloor pier.

Can I just knock the tube down to see if they rebuild it?

This is common advice and it is bad advice. Breaking the workings triggers the colony to abandon that route and re-enter elsewhere, often concealed. You lose the evidence and keep the termites.

What if the tube is dry and crumbling?

It may be old, but a dry tube does not prove the colony has gone: only that this route is not in use. Distinguishing old damage from current activity is a large part of what a professional inspection is for.

Sources

What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.

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