A Reddit user recently shared images of a mysterious dirt trail above a wall clock that grew into a large, soil-covered tunnel over 18 days. The structure was quickly identified by commenters as a termite mud tube, a troubling sign of an active termite infestation inside the home.

Termite mud tubes are narrow tunnels built from soil, wood, and saliva, primarily by subterranean termites. These pests use the tubes to travel between their underground nests and wood sources in homes while staying protected from air exposure, which they cannot survive for long. Finding these tunnels inside your home usually means termites have already penetrated the walls.

Termites are especially dangerous because they operate quietly and are hard to detect in early stages. By the time mud tubes appear, significant structural damage may have already begun. Colonies can number in the tens of thousands, and repairs often cost homeowners thousands of dollars. In fact, termites cause over $5 billion in annual damages in the U.S., most of which are not covered by insurance.

If you discover a mud tube indoors, don’t remove it right away. Breaking it can scatter the termites further or make them harder to locate. Instead, contact a licensed pest control expert who can identify the termite species, assess the extent of the damage, and recommend effective treatment options.

Treatments vary based on severity, ranging from bait systems and soil treatments to injections and full-home fumigation. Once termites are eliminated, prevention is key: reduce moisture, keep wood away from your home, seal entry points, and schedule annual inspections.

This Reddit case serves as a powerful reminder that small, odd details at home can signal much larger problems. Spotting a dirt trail may seem minor, but taking it seriously can prevent major damage and protect your home in the long term.