The term 'HILL-BUILDING BUG' refers to an ANT, which is a small insect that lives in colonies and is known for its ability to build hills or mounds of soil. Ants are social insects and have a complex division of labor within their colonies. They are also known for their ability to move large objects, such as stones and sticks, to build their hills. Ants are found all over the world and play an important role in the environment by aerating the soil and providing food for other animals.