Found these strange dirt-like veins running up my basement wall. They crumble when touched but seem hollow inside. Do I have a leak or something else?

These dirt-like veins are likely termite mud tubes, constructed by subterranean termites. Termites build these tubes as protective tunnels, allowing them to travel between their underground colonies and food sources, such as the wooden structures of your home. The tubes provide a controlled environment for the termites, maintaining humidity and protecting them from predators.

Typically, these tubes are about as wide as a pencil, ranging from 1/4 inch to 1 inch in diameter. They can extend several feet along walls and surfaces, often branching into complex networks. Unlike simple dirt or dust accumulations, these tubes have a distinct structure, with a clay-like texture that crumbles easily when touched.