Which of the following is a common sign of a termite infestation?

Mud tubes are a common sign of a termite infestation because they serve as protective passageways for termites. These tubes are constructed by subterranean termites using soil, wood particles, and their saliva, providing them with a safe route to travel between their underground nests and their food sources, which often include wood structures in a home. The presence of mud tubes indicates active termite activity, as they are integral to the termites' survival and movement.

While termite tunnels, wood dust, and fungal growth can also signal pest issues, they are less definitive indicators of a termite infestation specifically. Termite tunnels could refer to various tunnel-like structures created by different pests, wood dust, though associated with wood-destroying insects, can result from other pests or processes, and fungal growth typically points to moisture problems rather than directly indicating termite activity. Therefore, mud tubes uniquely highlight the presence and behavior of termites, making them a key sign when assessing for infestations.