What is a characteristic feature of exploratory tubes?

A characteristic feature of exploratory tubes is that they typically have a small exit hole. This is because exploratory tubes are constructed by certain wood-destroying insects, particularly termites, as they search for new food sources or nesting sites. The small exit hole serves as a way for the insects to access the surface while still maintaining a degree of concealment and protection from predators.

The other options describe different aspects that do not pertain to exploratory tubes specifically. While exploratory tubes may be weaker than other types, such as utility tubes, the focus on their small exit hole is key to understanding their function and how they are utilized by termites during their exploration activities.