Mud Tubes: Working, Exploratory, Drop and Swarm
Why this matters
A mud tube is the most common piece of termite evidence a tech finds, and the one most often misread. A tube tells you three things if you read it properly: what the termites were doing when they built it, whether they are still using it, and where the rest of the colony's activity probably is. Read it lazily and you either sell a treatment for a twenty-year-old abandoned tube, or you write "old tubes, no activity" on a house where the colony is feeding in the wood two feet above. This card owns tube reading. The full inspection sequence lives in Inspect for Active Termite Activity.
What a tube is for
Subterranean termite workers dry out quickly in open air and avoid light. When they have to cross a surface they cannot tunnel through (a concrete footing, a block wall, a pipe, open air under a floor), they build a shelter of soil, chewed wood, saliva and fecal material. The tube keeps humidity in, keeps predators and light out, and connects the soil, where the colony gets moisture, to the wood it eats. Every tube type is a variation on that one purpose, built for a different job.
The four tube types
===subfloor and joists=========================
===sill plate====+ |
| | | | drop tube,
| | working | | | | built down
| | tube, wide, | | | explor-| from joist,
| | flat, soil | \ / atory, | ends short
| | to sill | || thin, | of the soil
| | | || branch-|
| | swarm | || ing, |
| | castle, | || dead |
| | slits [=] | || ends |
+--+-------------+-------++------soil----------
foundation wall crawlspace floor
Working tube (shelter tube). Runs from the soil up a surface to wood: up a foundation wall to the sill, up a pier to a beam, along a plumbing line to the subfloor. Usually flat against the surface, wider than a pencil, often wider still where traffic is heavy, and sometimes two or three tubes run side by side. It is a commuter road. When active, it means the colony is going back and forth between soil and a food source in the structure.
Exploratory tube. Thinner, more fragile, often branching, and rising from the soil (up a wall or freestanding off the crawlspace floor) without obviously reaching wood. Many end in open air. It is foragers searching for food. Exploratory tubes are often abandoned when the search fails, so they are frequently found empty and crumbling. Their presence says a colony is close and probing; it does not by itself say the colony has reached wood.
Drop tube. Built from the wood down toward the soil, often hanging free from a joist or subfloor, sometimes stopping short of the ground. Drop tubes are often lighter in color because they carry more chewed wood. The important thing is direction: termites built it from above, which means they were already in the wood above it. A drop tube is a pointer to infested wood overhead, usually termites returning toward soil moisture or opening a second route.
Swarm castle (swarm tube). A short, wide earthen structure built at the point where winged reproductives (swarmers) will leave, with narrow slits for them to exit. Found around slab cracks, at the base of walls, on a basement floor joint or on wood surfaces near emergence points, usually in the swarm season for your local species. Workers build them for the colony's mature reproductives, so they mean a colony large and old enough to swarm. Inside a structure, they mean that colony is under or in it.
Active or old: the break test
Do not read activity from color or texture alone. Fresh tubes are often darker and damp-looking and old ones pale and crumbly, but a dry crawlspace makes a live tube look old, and a damp one keeps an abandoned tube dark. The reliable test is mechanical.
- Photograph the tube first. On a real estate inspection especially, the tube is evidence; record its location and condition before you disturb it.
- Break a short section near the middle, about an inch, with a probe or screwdriver tip. Breaking the middle rather than the top or bottom leaves both ends attached, so a repair is easy to recognize.
- Look inside immediately. Live workers (soft, cream-colored, wingless) or soldiers (with enlarged, darker heads and mandibles) moving in the broken ends mean the tube is in use today. A moist, clean interior with no insects is inconclusive: the termites may simply not be in that section at that moment.
- Return and look for repair. An active tube is usually repaired within days, with new, darker material bridging the gap. Mark the spot (photo, distance from a corner) so you can find it again. No repair on the return visit is evidence the tube is not in use, not proof the colony is gone.
What a negative break test does not prove. An empty, unrepaired tube says only that this path is not in use. Colonies abandon tubes when treated soil, a dried-out route or a better path makes them switch. The colony may be entering 10 feet away through a slab joint you cannot see, or feeding in the wood the tube used to reach. Probe the wood at the top of every tube, active or not. See related: How to Probe and Sound Wood for Hidden Termite Damage.
Worked example: an annual crawlspace inspection
A route customer under a bait or liquid service agreement gets an annual crawlspace inspection. Before entry the tech checks for water near wiring and for rodent droppings, handled as in Foundation Types and Where Termites Get In. Inside, he finds three things.
- On the third pier from the east wall: a working tube, about the width of a finger, running from soil to the beam. Dark and damp.
- On the north foundation wall: two exploratory tubes, thin and branched, rising about 18 inches from the soil and ending in open air. Pale and dry.
- Under the hall bathroom: a drop tube hanging from the subfloor near the toilet flange, about 10 inches long, stopping well short of the soil. Light tan.
The break test, day one. The tech photographs all four tubes, breaks an inch from the middle of the pier tube and sees workers moving in both ends. He breaks the drop tube near its middle: dry, empty. He leaves the exploratory tubes alone apart from photos; they are fragile and already reading as abandoned, and breaking them adds nothing he can interpret.
What each tube suggests before the return visit. The pier tube is active on day one, so there is a live foraging route into the beam. The exploratory tubes say foragers were probing the north wall at some point, with no sign they found anything. The drop tube is the one to worry about despite being empty: it was built down from the subfloor, so termites were in the wood under that bathroom at some point. A leaking toilet flange and a damp subfloor are exactly the conditions that let a colony live in wood above ground, and a moisture problem there goes on the conducive conditions record. See related: Moisture and Conducive Condition Report.
The probe. At the top of the pier tube, the beam sounds solid but the probe goes in a quarter inch into soft galleries along one face. Around the drop tube, the subfloor near the flange is soft and delaminating; the probe finds galleries with no live termites visible.
The return, five days later. The pier tube is repaired with a darker band across the break. The drop tube is unrepaired.
The read. An active colony is using the pier route into the beam. The subfloor under the bathroom was infested; whether it still is cannot be settled from the drop tube, because an unrepaired drop tube means only that the termites are not using that path. The record says exactly that: active tube at pier 3 confirmed by repair, damage in beam; damage and old drop tube at bathroom subfloor, activity not confirmed; moisture at toilet flange. The service response to that activity follows the agreement and the product labels; this card stops at the reading.
What would change the read. If the drop tube had been repaired too, there would be two active sites, and the bathroom would no longer be a historical note. If the pier tube had been empty on day one and unrepaired on the return, the account would have no confirmed live activity at all, and the tech would be writing damage and old tubes, with the bathroom moisture as the most likely place for a future problem.
Mistakes that cost you
Knocking every tube down before photographing. The next tech, or the inspector for a buyer, has nothing to compare against. Photograph first; break only a section.
Reading a tube's absence as clearance. On slab homes and finished basements, the working tubes are often behind cladding, under flooring or inside block cores. No tube on a visible wall says nothing about the walls you cannot see. See related: Foundation Types and Where Termites Get In.
Calling a tube "active" on a damp look. Write active only when you saw live termites or a repair. Everything else is "tube present, activity not confirmed" with the date of your break and the date of your recheck. On a WDI report, live insects get their own box for this reason; see The WDI Report Form, Section by Section.
Confusing other builders. Mud dauber wasp nests are earthen too, but they are built as tubes or cells attached to a surface with no connection to soil, often high on walls, eaves or garage rafters, and they are hard and smooth rather than granular. A tube that does not connect toward soil or wood in any direction, high on a wall, is worth a second look before it goes on a report.
References
- See related: Inspect for Active Termite Activity
- See related: How to Probe and Sound Wood for Hidden Termite Damage
- See related: Foundation Types and Where Termites Get In
- See related: Moisture and Conducive Condition Report
- See related: Pest Activity Signs Reference